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Chicago Manual of Style Author-Date Citations and Reference Lists

Rev. 4 February 2025

This tutorial is a quick guide to Chicago Manual of Style (CMOS) author-date citations and bibliographic references, based on the eighteenth edition. References to specific requirements in the printed source are included in this text as (chapter.paragraph).

Note that CMOS author-date style, which is commonly used in the sciences and social sciences, is different from CMOS notes and bibliography style, which is more-commonly used in the humanities.

This style is important to geographers because it is the citation style commonly used by geography journals such as the Annals of the American Association of Geographers, the flagship publication of the premier professional society of geographers in the United States.

General Format

Citations

As the name implies, citations are made using the author's last name and the date (year) of publication, with no punctuation between the name and year.

(Lastname Year)

Citations can also be made when the author's name is used in the text by following the name with the year in parentheses (CMOS 13.116):

Lastname (Year) found that...

Multiple sources can be included in a single parenthetical citation by separating the sources with semicolons (CMOS 13.116):

(Lastname1 Year1; Lastname2 Year2; Lastname3 Year3)

Reference List Entries

Author-date citations provide abbreviated information about cited sources that can be conveniently included in the flow of the text.

The general format for CMOS author-date bibliographic references is:

Lastname, Firstname. Year. "Title." Publication_Info.

Web Pages

The author for a web page should be the author listed on the web page. If no author is listed on a web page, the name of the organization publishing that page should be used as the author (CMOS 14.104). Web pages with no clear organizational source or authorship should be avoided in academic writing.

When an organization is commonly referred to with an acronym, that acronym may be used in place of the full name in the citation, with the acronym included in parenthesis in the reference list entry following the full name of the organization.

The year in the citation and reference list should be the date when the page indicates that it was last modified or updated.

If the web page does not list the date when the content was last updated, use "n.d." as the year and provide an "Accessed" month and day (CMOS 14.104).

Citations

"CMOS author-date citation format is of special interest to geographers because it is similar to the citation style used in The Annals of the Association of American Geographers, the flagship publication of the premier professional society of geographers in the United States" (Minn 2025).

A stroke can either be an ischemic stroke, where a clot obstructs blood flow in the brain, or a hemorrhagic stroke, where a blood vessel ruptures and can not provide blood flow in the brain (American Stroke Association n.d.).

The CDC began operation in 1946 as Communicable Disease Center, with a focus on malaria prevention. The CDC is an agency under the US Department of Health and Human Services (HHS) and is headquartered in Atlanta, GA (CDC 2019).

Reference List

Minn, Michael. 2025. "Chicago Manual of Style Author-Date Citations and Reference Lists." Modified 24 January. http://michaelminn.net/tutorials/cmos-citation.

American Stroke Association. n.d. "About Stroke." Accessed 15 July 2019. https://www.strokeassociation.org/en/about-stroke.

Centers for Disease Control and Prevention (CDC). 2019. "Our History - Our Story." Modified 7 July. https://www.cdc.gov/about/history/.

Journals Articles (Single Author)

A journal is "a scholarly or professional periodical available mainly by subscription" (CMOS 14.65) and articles in journals are generally subject to peer-review by two or three experts in the field who evaluate and approve articles for publication.

References to articles from peer-reviewed journals follow this general format :

Lastname, Firstname. Year. "Article Title." Journal Name Volume (Issue): Page - Page. URL.

Article titles should be enclosed in quotation marks and use title case (CMOS 14.68). Note that this is different from APA style where journal article titles are in sentence case.

Journal titles should be italicized and use title case (CMOS 14.69). When using media where italics are unavailable, asterisks (*) surrounding the text can be substituted, although this can be distracting (CMOS 7.53).

Digital Object Identifier (DOI) URLs should be included for journal articles whenever possible to make it easier for readers to access those articles.

Citations

Much of the attraction of passenger rail may be attributed to a nostalgic longing for an imagined simpler time, with that nostalgia manifesting the alienation and continual threat of creative destruction inherent in capitalism (Minn 2013).

Vogel (2017) identified 55 chemicals released during the fracking process that are associated with increased cancer risk.

Reference List

Minn, Michael. 2013. "The Political Economy of High Speed Rail in the United States." Mobilities 8 (2): 185-200. https://dx.doi.org/10.1080/17450101.2012.655973.

Vogel, Lauren. 2017. "Fracking Tied to Cancer-Causing Chemicals." Canadian Medical Association Journal 189 (2): E94 - E95. DOI: 10.1503/cmaj.109-5358.

Journal Articles (Multiple Authors)

Citations of articles with two authors include both author last names separated by "and."

Citations of articles with three or more authors list the first author's name followed by et al., which is the abbreviation for the Latin phrase et alia, meaning and others. Note that previous editions of CMOS specified the use of et al. with four or more authors (CMOS 13.23) Et al. is considered a "common" Latin abbreviation that is not normally italicized in the manner used for words borrowed from other languages (CMOS 7.57).

Reference list entries for articles, regardless of the number of authors, always include all full author names. The first author is listed last (family) name first, with subsequent authors listed with the given (first) name first. The conjunction and with the Oxford comma is placed before the final author's name (CMOS 13.78).

Author names are separated by commas with an "and" placed before the last name. Reference list author lists use the serial (Oxford) comma, even when there are only two authors (CMOS 2024).

Citations

The Getis-Ord GI* statistic (Getis and Ord 1992) identifies areas with high values that are also surrounded by high values. However, unlike simple observation or techniques like kernel density analysis, this algorithm uses statistical comparisons of all areas to create p-values indicating how probable it is that clusters of high values in a specific areas could have occurred by chance.

Campbell et al. (2009) found that transportation provided with electricity produced with biomass considerably outperformed transportation fueled by cellulosic ethenol, with bioelectricity producing "an average of 81% more transportation kilometers and 108% more emissions offsets per unit area of cropland than does cellulosic ethanol."

Jacobson et al. (2012) found that when discussions of decision making errors were incorporated in the history curriculum of high school students, their performance of a subsequent test of rationality also improved - and helped their retention of historical facts as well.

Yang et al. (2000) found increased lung cancer mortality associated with petroleum refineries, but no association with abnormal birth sex ratios.

Reference List

Campbell, J. Elliott, David B. Lobell, and Christopher B. Field. 2009. "Greater Transportation Energy and GHG Offsets from Bioelectricity than Ethanol." Science 324 (5930): 1055-1057. https://dx.doi.org/10.1126/science.1168885.

Getis, Arthur, and J.K. Ord. 1992. "The Analysis of Spatial Associations by Use of Distance Statistics." Geographical Analysis 24 (3): 189-206. https://dx.doi.org/10.1111/j.1538-4632.1992.tb00261.x.

Jacobson, David, Andrew Parker, Chris Spetzler, Wandi Bruine de Bruin, Keith Hollenbeck, David Heckerman, and Baruch Fischhoff. 2012. "Improved Learning in U.S. History and Decision Competence with Decision-Focused Curriculum." Plos One 7 (9): e45775. https://dx.doi.org/10.1371/journal.pone.0045775.

Yang, Chun-Yuh, Bi-Hua Cheng, Te-Yao Hsu, Shang-Shyue Tsai, Chung-Feng Hung, and Trong-Neng Wu. 2000. "Female Lung Cancer Mortality and Sex Ratios at Birth near a Petroleum Refinery Plant." Environmental Research 83 (1): 33-40. https://dx.doi.org/10.1006/enrs.2000.4038.

Grey Literature

Grey literature refers to research reports, working papers, and white papers that are produced by organizations outside of traditional academic publishing channels and generally not subject to peer-review.

Citations

In 2016, light-duty vehicles accounted for 58.5% of transportation energy use while medium/heavy-duty trucks and buses accounted for 23.9% (Davis and Boundy 2018).

One of the dominant bus companies in the United State is actually a British firm, FirstGroup. In 2019. FirstGroup made a quarter of its £7,126.9m revenue and almost half its £332.9m operating profit from its school bus division, First Student, with another 3% of profits coming from America's only remaining national commercial bus line, Greyhound (FirstGroup plc. 2020, 6).

Reference List

Davis, Stacy C. and Robert G. Boundy. 2019. "Transportation Energy Data Book: Edition 37.1." Oak Ridge, TN: Oak Ridge National Laboratory. Modified 15 July 2019. https://www.ornl.gov/content/transportation-energy-data-book.

FirstGroup plc. 2020. "Annual Report and Accounts 2081." Modified 15 July 2020. https://www.firstgroupplc.com/investors/annual-report-2019.aspx.

Wikipedia

Wikipedia is an open, online encyclopedia. Although Wikipedia is not considered an authoritative source, numerous studies have found Wikipedia articles as reliable as more-authoritative sources like Encyclopedia Britannica, although there are notable exceptions, such as the articles for politicians and celebrities.

Because Wikipedia articles are collectively created, there is no stable, single author, so the author should be given as Wikipedia.

Because Wikipedia articles are constantly subject to revision, a last modified date is needed in the reference list (CMOS 14.131).

Citation

The "Stroke Belt" is an informal name given to a nine-state region in the Deep South that has unusually high rates of stroke and other cardiovascular diseases (Wikipedia 2024).

Reference List

Wikipedia. 2024. "Stroke Belt." Modified September 26. https://en.wikipedia.org/wiki/Stroke_Belt.

Magazines and Newspapers

Reference list entries for magazines and newspapers should include the name of the publication and the date of publication listed on the website.

For publications that do not give by-lines (authors), the name of the publication should be used as the author.

Citations

While commercial airliners are getting larger, the airlines are also finding ways to increase revenue by adding more seats and maximizing load factors, reducing the amount of room per passenger (Bradley 2018).

States with higher rates of behavioral risk factors (like smoking) also tend to have higher cancer incidence and death rates, with access to medical care and demographics also being contributors (Cook 2018).

While the trade war with China has clearly hurt their exports, annual growth in 2Q 2019 was still an impressive 6.2%. This indicates that China's massive economy is now driven by domestic demand, and hints that further trade pressures will have limited influence on China's behavior (The Economist 2019).

Reference List

Bradley, Ryan. 2018. "Why Bigger Planes Mean Cramped Quarters." Popular Science, 22 August. https://www.popsci.com/why-no-personal-space-huge-airplanes.

Cook, Lindsey. 2015. "You're Most Likely to Die From Cancer in 1 of These States." US News and World Report, 15 October. https://www.usnews.com/news/blogs/data-mine/2015/10/15/youre-most-likely-to-die-from-cancer-in-1-of-these-states.

The Economist. 2019. "China’s Growth is the Slowest in Nearly Three Decades: Get Used To It." 15 July. https://www.economist.com/finance-and-economics/2019/07/15/chinas-growth-is-the-slowest-in-nearly-three-decades-get-used-to-it.

Books

Books sources are listed with a city of publication and the name of the publisher.

Reprints of classic works often include the year of original publication in square brackets in the citation and in parenthesis in the reference list entry (CMOS 14.16).

Citations to specific information or quotations in books should also include the page number(s), separated from the author and year by a comma.

Book titles are italicized and title case in reference lists (CMOS 13.107).

Citations

The initial use of GIS in public health was largely driven by US federal government agencies starting in the mid 1970s (Cromley and McLafferty 2012, 35).

Marx ([1867] 1906, 259) notes that while the capitalist has the right to make the working day as long as possible to maximize profit, the worker has the right to withhold services to limit the duration of the working day. Since these rights are nominally equal under free exchange, "Between equal rights force decides," and the capitalist will use other means to coerce additional hours from labor.

Shand (1993, 148) notes that although Kant was sociable and enjoyed the company of women, he was the stereotypical "self-contained philosophical speculator" and never married.

Reference List

Cromley, Ellen and Sara McLafferty. 2012. GIS and Public Health, second edition. New York: Guilford Press.

Marx, Karl. (1867) 1906. Capital: A Critique of Political Economy. Translated from the third German edition by Samuel Moore and Edward Aveling. Edited by Frederick Engels. Revised and amplified according to the fourth German edition by Ernest Untermann. New York: Charles H. Kerr and Company.

Shand, John. 1993. Philosophy and Philosophers: An Introduction to Western Philosophy. Montreal: McGill-Queen's University Press.

Data Sources

Although CMOS author-date citations are intended for citation of textual information, they can also be used to cite data sources.

Citations

Median age by county, 2019-2023 (USCB n.d.)
2010-2014 Overall Cancer Rates by County (CDC 2018)
Nuclear Power Plants in the USA (EIA 2018)

Reference List

Centers for Disease Control and Prevention and The National Cancer Institute (CDC). 2018. "State Cancer Profiles, Incidence Rate Report for United States by County, 2010-2014." Modified 15 May. https://www.statecancerprofiles.cancer.gov/incidencerates/.

US Census Bureau (USCB). n.d. "2023 American Community Survey Five-year Estimates, Table B01002." Accessed 24 January 2025. https://data.census.gov.

US Energy Information Administration (EIA). 2018. "U.S. Power Plants." Modified May 15. https://www.eia.gov/maps/layer_info-m.php.

Common Form Problems With CMOS Author-Date Citations

Multiple Articles by the Same Author in the Same Year

Two or more works by the same author in the same year must be differentiated by the addition of lower case letters after the year to both the citation and reference list entries. Ordering of letters should be in alphabetical ordering of the titles (CMOS 13.114).

Problem

Krugman asserts that tariffs will inhibit rather than incentivize the return of manufacturing to the US because investors will be loathe to make substantial sunk investments in manufacturing infrastructure when the government demonstrates that trade agreements are now subject to the uncertain whims of whoever is president (Krugman 2025). However, Krugman hypothesizes that the president's actions are less about restoring US manufacturing than projecting dominance and rewarding wealthy donors (Krugman 2025).

Krugman, Paul. 2025. "How To Damage US Manufacturing." Modified 27 January. https://paulkrugman.substack.com/p/how-to-damage-us-manufacturing.

Krugman, Paul. 2025. "Why Has Trump Gone Soft on China and Hard on Canada?" Modified 2 February. https://paulkrugman.substack.com/p/why-has-trump-gone-soft-on-china.

Solution

Krugman asserts that tariffs will inhibit rather than incentivize the return of manufacturing to the US because investors will be loathe to make substantial sunk investments in manufacturing infrastructure when the government demonstrates that trade agreements are now subject to the uncertain whims of whoever is president (Krugman 2025a). However, Krugman hypothesizes that the president's actions are less about restoring US manufacturing than projecting dominance and rewarding wealthy donors (Krugman 2025b).

Krugman, Paul. 2025a. "How To Damage US Manufacturing." Modified 27 January. https://paulkrugman.substack.com/p/how-to-damage-us-manufacturing.

Krugman, Paul. 2025b. "Why Has Trump Gone Soft on China and Hard on Canada?" Modified 2 February. https://paulkrugman.substack.com/p/why-has-trump-gone-soft-on-china.

Use of Website Format for a Journal, Magazine, or Newspaper Article

While journals almost universally make their articles accessible through the internet, and articles can be published on multiple websites, journal articles should still be cited and referenced in journal format (preferably with a DOI URL) rather than as if they were non-peer-reviewed websites.

Problem

Minn, Michael. 2019. "Contested Power: American Long-Distance Passenger Rail and the Ambiguities of Energy Intensity Analysis." Accessed 21 September 2019. https://doi.org/10.3390/su11041200.

Solution

Minn, Michael. 2019. "Contested Power: American Long-Distance Passenger Rail and the Ambiguities of Energy Intensity Analysis." Sustainability 11 (4): 1200. https://doi.org/10.3390/su11041200.

Closing Punctuation Outside Quotation Marks

In the United States, when using punctuation following quoted text, the punctuation goes inside the closing quotation mark. This seemingly illogical practice (which is not used in Britain) dates from a time when fonts used for printing had fixed-width characters, and placing the punctuation after the quotation mark created an unattractive gap between the end of the text and the punctuation (MLA Style Center 2020, CMOS 6.9).

However, when providing a parenthetical citation at the end, the citation is part of the sentence and the closing punctuation follows the citation.

Problem

Centers for Disease Control and Prevention (CDC). 2019. "Arthritis Risk Factors". Modified 1 October. https://www.cdc.gov/arthritis/basics/risk-factors.htm.

Solution

Centers for Disease Control and Prevention (CDC). 2019. "Arthritis Risk Factors." Modified 1 October. https://www.cdc.gov/arthritis/basics/risk-factors.htm.

Ordering and Punctuation of Multiple Authors

Problem

Nguyen, J., Ziser, K.E.D., Penm, J., Schneider, C.R.. 2019. "Impact of a Pharmacy Technician on Clinical Pharmacy Services in an Australian Hospital." International Journal of Clinical Pharmacy 41 (2): 445–451. https://doi.org/10.1007/s11096-019-00801-x.

Nguyen, Jessica T.V., Kate E. D. Ziser, Jonathan Penm, Carl R. Schneider. 2019. "Impact of a Pharmacy Technician on Clinical Pharmacy Services in an Australian Hospital." International Journal of Clinical Pharmacy 41 (2): 445–451. https://doi.org/10.1007/s11096-019-00801-x.

Solution

Nguyen, Jessica T.V., Kate E. D. Ziser, Jonathan Penm, and Carl R. Schneider. 2019. "Impact of a Pharmacy Technician on Clinical Pharmacy Services in an Australian Hospital." International Journal of Clinical Pharmacy 41 (2): 445–451. https://doi.org/10.1007/s11096-019-00801-x.

Formatting Borrowed From Other Citation Styles

Problem

Census.gov. (2019). [online] Available at: https://www.census.gov/content/dam/Census/library/publications/2018/acs/acs_general_handbook_2018_ch09.pdf [Accessed 23 Sep. 2019].

Nguyen, Jessica T.V., Kate E. D. Ziser, Jonathan Penm, Carl R. Schneider. April 2019. "Impact of a pharmacy technician on clinical pharmacy services in an Australian hospital." International Journal of Clinical Pharmacy, Volume 41, Issue 2, pp 445–451. https://doi.org/10.1007/s11096-019-00801-x.

Nguyen, J. T., Ziser, K. E., Penm, J., & Schneider, C. R. (2019). Impact of a pharmacy technician on clinical pharmacy services in an Australian hospital. International Journal of Clinical Pharmacy, 41(2), 445-451. (APA style)

Nguyen, Jessica TV, et al. "Impact of a pharmacy technician on clinical pharmacy services in an Australian hospital." International Journal of Clinical Pharmacy 41.2 (2019): 445-451. (MLA style)

Solution

US Census Bureau. 2019. "Differences Between the ACS and the Decennial Census." Modified 23 September. https://www.census.gov/content/dam/Census/library/publications/2018/acs/acs_general_handbook_2018_ch09.pdf.

Nguyen, Jessica T.V., Kate E. D. Ziser, Jonathan Penm, Carl R. Schneider. 2019. "Impact of a Pharmacy Technician on Clinical Pharmacy Services in an Australian Hospital." International Journal of Clinical Pharmacy 41 (2): 445–451. https://doi.org/10.1007/s11096-019-00801-x.

Missing Period Separators

Problem

Department of Environmental Conservation (DEC). 2019. "State Superfund Sites: Inactive Hazardous Waste Disposal Site Program" Modified 11 November. https://www.dec.ny.gov/chemical/8439.html.

Oregon Health Authority, 2014. "Chlamydia." Modified October 15. https://www.oregon.gov/oha/PH/DISEASESCONDITIONS/COMMUNICABLEDISEASE/REPORTINGCOMMUNICABLEDISEASE/REPORTINGGUIDELINES/Documents/chlamydia.pdf.

Merriam-Webster, 2019 "demographic." Modified 24 Sept. https://www.merriam-webster.com/dictionary/demographics.

Solution

Department of Environmental Conservation (DEC). 2019. "State Superfund Sites: Inactive Hazardous Waste Disposal Site Program." Modified 11 November. https://www.dec.ny.gov/chemical/8439.html.

Oregon Health Authority. 2019. "Chlamydia." Modified October 15. https://www.oregon.gov/oha/PH/DISEASESCONDITIONS/COMMUNICABLEDISEASE/REPORTINGCOMMUNICABLEDISEASE/REPORTINGGUIDELINES/Documents/chlamydia.pdf.

Merriam-Webster. 2019. "demographic." Modified 24 September. https://www.merriam-webster.com/dictionary/demographics.