CSE Citation Style: Three Systems With Examples

What CSE style is and where it is used

CSE stands for the Council of Science Editors, the organization that maintains Scientific Style and Format: The CSE Manual for Authors, Editors, and Publishers. The manual covers scientific writing, terminology, data presentation, and citation practices. A course that requests “CSE style” usually means one of the manual’s three citation systems.

CSE is common in biology, ecology, zoology, botany, genetics, microbiology, agriculture, environmental science, and related laboratory fields. Some public health and medical courses also use it, although health-sciences journals may instead require Vancouver, AMA, or a journal-specific style.

No discipline uses CSE universally. For example, one ecology course may require name-year citations such as “(Chen 2023),” while another may require citation-sequence numbers such as “¹.” The assignment or publication rules control the choice.

How to identify the required CSE system

Look for the terms “citation-sequence,” “name-year,” or “citation-name” in the assignment sheet. Abbreviations such as C-S, N-Y, and C-N may also appear. If the instructions only say “CSE,” compare any sample paper or reference list with the patterns below. Ask the instructor if no sample identifies the system.

• Citation-sequence: Sources receive numbers in the order they first appear. The first source cited is 1, even if its author would appear last alphabetically.
• Name-year: In-text citations contain an author name and year, such as “(Patel 2022).” The reference list is alphabetical and unnumbered.
• Citation-name: The reference list is alphabetized first and then numbered. In-text citations use those assigned numbers, so the first source cited may be 4 or 17.
• Weak: “CSE uses numbers, so I numbered the references alphabetically.” Strong: Determine whether the assignment says citation-sequence or citation-name; both use numbers, but only citation-name alphabetizes before assigning them.
• Weak: “The sample uses author and year, so I formatted it like APA.” Strong: Use CSE name-year punctuation: “(Patel 2022),” not APA’s “(Patel, 2022).”

In-text citations in all three CSE systems

Citation-sequence uses a superscript Arabic number for each source. Assign the number when the source first appears and reuse that number every time the same source is cited. For example: “Repeated heat exposure can reduce coral recovery.¹” If the same study appears later, cite it as ¹ again rather than assigning a new number.

Name-year places the author’s surname and publication year in parentheses without a comma: “Coral recovery varies among regions (Garcia 2022).” When the author appears in the sentence, place only the year in parentheses: “Garcia (2022) reported regional differences.”

For two authors, name both: “(Garcia and Patel 2022).” For three or more authors, use the first author followed by “et al.”: “(Garcia et al. 2022).” Separate multiple sources with semicolons: “(Chen 2019; Garcia and Patel 2022; Wong 2024).” Follow the assigned CSE edition or course guide when ordering multiple citations within one set of parentheses or adding page numbers for quotations, because local implementations can differ slightly in those details.

• Citation-sequence weak: “The first discussion of the study uses ¹, but the second uses ⁵.” Citation-sequence strong: “Both discussions use ¹ because they refer to the same source.”
• Name-year weak: “Pollinator diversity declined (Garcia, 2022).” Name-year strong: “Pollinator diversity declined (Garcia 2022).”
• Name-year weak: “Pollinator diversity declined (Garcia, Patel, & Wong, 2022).” Name-year strong: “Pollinator diversity declined (Garcia et al. 2022).”
• Citation-name example: An alphabetized list contains Alvarez as reference 1, Chen as reference 2, and Rivera as reference 3. If Rivera is cited first in the paper, the first in-text marker is ³—not ¹.
• Citation-name weak: “I assigned Rivera 1 because it was cited first.” Citation-name strong: “Rivera remains 3 because citation-name numbers come from the alphabetized list.”

Reference list order for each CSE system

The systems differ most clearly in the reference list. Suppose a paper cites Rivera first, Adams second, and Chen third. Citation-sequence lists Rivera as 1, Adams as 2, and Chen as 3 because that is their order of first use.

Citation-name alphabetizes the same sources before assigning numbers: Adams becomes 1, Chen becomes 2, and Rivera becomes 3. The paper therefore cites Rivera as ³ even though Rivera is the first source mentioned.

Name-year also alphabetizes Adams, Chen, and Rivera, but it does not number them. For several works by the same author, arrange entries by year according to the required CSE manual or course guide. Distinguish same-author, same-year works with letters when required, such as 2022a and 2022b.

• Citation-sequence: numbered; arranged by first appearance in the text.
• Name-year: unnumbered; arranged alphabetically by author.
• Citation-name: numbered; arranged alphabetically by author before numbers are assigned.
• Weak citation-sequence list: “1. Adams; 2. Chen; 3. Rivera,” even though Rivera is cited first. Strong citation-sequence list: “1. Rivera; 2. Adams; 3. Chen.”
• Weak citation-name list: “1. Rivera; 2. Adams; 3. Chen,” following citation order. Strong citation-name list: “1. Adams; 2. Chen; 3. Rivera,” following alphabetical order.
• Use a heading such as “References” and place each source in a separate entry. Follow the instructor’s specifications for spacing and hanging indents because course and journal layouts can vary.

How CSE reference entries are constructed

CSE normally gives authors as surname followed by initials, without periods between the initials: “Fang FC,” not “Fang, F. C.” Article and chapter titles use sentence-style capitalization. Numbered CSE systems place the year later in the entry, while name-year places it immediately after the authors.

Citation-sequence and citation-name use the same basic entry format. Their difference is the order in which entries receive numbers. The examples below therefore label both as “numbered systems.”

• Journal article, numbered systems: “1. Fang FC, Steen RG, Casadevall A. Misconduct accounts for the majority of retracted scientific publications. Proc Natl Acad Sci U S A. 2012;109(42):17028-17033. doi:10.1073/pnas.1212247109.”
• Journal article, name-year: “Fang FC, Steen RG, Casadevall A. 2012. Misconduct accounts for the majority of retracted scientific publications. Proc Natl Acad Sci U S A. 109(42):17028-17033. doi:10.1073/pnas.1212247109.”
• Book, numbered systems: “1. Alberts B, Johnson A, Lewis J, Morgan D, Raff M, Roberts K, Walter P. Molecular biology of the cell. 6th ed. New York (NY): Garland Science; 2015.”
• Book, name-year: “Alberts B, Johnson A, Lewis J, Morgan D, Raff M, Roberts K, Walter P. 2015. Molecular biology of the cell. 6th ed. New York (NY): Garland Science.”
• Book chapter, numbered systems: “1. Rojko JL, Hardy WD. Feline leukemia virus and other retroviruses. In: Sherding RG, editor. The cat: diseases and clinical management. New York (NY): Churchill Livingstone; 1989. p. 229-332.”
• Book chapter, name-year: “Rojko JL, Hardy WD. 1989. Feline leukemia virus and other retroviruses. In: Sherding RG, editor. The cat: diseases and clinical management. New York (NY): Churchill Livingstone. p. 229-332.”
• Website model, numbered systems: “1. Great Lakes Research Center. Harmful algal bloom monitoring [Internet]. Ann Arbor (MI): Great Lakes Research Center; 2024 Sep 3 [updated 2024 Oct 1; cited 2025 Jan 15]. Available from: https://example.org/algal-blooms.” This is an illustrative source showing the required fields.
• Website model, name-year: “Great Lakes Research Center. 2024 Sep 3. Harmful algal bloom monitoring [Internet]. Ann Arbor (MI): Great Lakes Research Center; [updated 2024 Oct 1; cited 2025 Jan 15]. Available from: https://example.org/algal-blooms.”
• Weak numbered journal entry: “Fang, F. C., Steen, R. G., & Casadevall, A. (2012). Misconduct accounts for the majority of retracted scientific publications.” Strong: Use CSE author initials, journal details, year placement, page range, and DOI as shown in the complete numbered example.
• Weak name-year book entry: “Alberts B, et al. Molecular biology of the cell. 2015.” Strong: Put 2015 after the authors and include the edition, publication place, and publisher.

Journal title abbreviations in CSE references

CSE usually abbreviates journal titles. Do not invent an abbreviation by shortening words yourself. Search the journal’s full title or ISSN in the NLM Catalog and copy the listed NLM Title Abbreviation. For journals not covered there, use the abbreviation source specified by the instructor or journal, such as an ISO 4-based title list.

CSE journal abbreviations normally omit periods within the abbreviated title. The reference still has a period after the journal title as part of the citation’s punctuation. A one-word journal title such as “Nature” normally remains unchanged.

• Full title: “Proceedings of the National Academy of Sciences of the United States of America.” CSE abbreviation: “Proc Natl Acad Sci U S A.”
• Weak: “J. Exp. Bio.” Strong: “J Exp Biol,” the recognized abbreviation for Journal of Experimental Biology.
• Weak: “International Journal of Molecular Sciences” copied in full without checking. Strong: Search the NLM Catalog by title or ISSN and use “Int J Mol Sci.”
• Weak: “PNAS” because that abbreviation appears on the journal’s website. Strong: “Proc Natl Acad Sci U S A” when the required CSE source list uses the NLM abbreviation.

How CSE differs from APA style

APA uses one author-date system, while CSE offers author-date and two numbered systems. CSE name-year may resemble APA, but its punctuation and reference construction are different. For example, CSE writes “(Nguyen 2023),” while APA writes “(Nguyen, 2023).”

APA reference lists are always alphabetical. CSE lists are alphabetical in name-year and citation-name, but citation-sequence follows first appearance. APA also writes author initials with periods, uses an ampersand before the final author, and normally spells out journal titles. CSE commonly uses compact initials and abbreviated journal titles.

• CSE name-year: “Nguyen PT, Hall M. 2023. Microbial responses to soil warming. J Exp Biol. 226(4):1-9.”
• APA pattern: “Nguyen, P. T., & Hall, M. (2023). Microbial responses to soil warming. Journal of Experimental Biology, 226(4), 1–9.”
• Weak: “CSE name-year is APA without italics.” Strong: Treat it as a separate system with CSE punctuation, author initials, year placement, journal abbreviations, and reference ordering.

Incorrect and correct CSE entries compared

Each pair starts with a reference formatted the way students usually guess, followed by the entry CSE actually requires.

Common mistakes and how to fix them

Mixing name-year and numbered citations, such as using “(Chen 2022)” in one paragraph and “³” in another.

Choose the assigned CSE system and apply it throughout the paper and reference list.

Writing a CSE name-year citation as “(Chen, 2022).”

Remove the APA-style comma: “(Chen 2022).”

Assigning a new citation-sequence number whenever a previously cited source reappears.

Reuse the number assigned when the source first appeared.

Alphabetizing a citation-sequence reference list.

Arrange citation-sequence references by first appearance in the text.

Arranging a citation-name reference list by first appearance.

Alphabetize the references first, assign numbers to that list, and use those numbers in the text.

Copying a journal’s full title or inventing a shortened form.

Use the recognized abbreviation, usually found through the NLM Catalog. For example, use “J Exp Biol,” not “J. Exp. Bio.”

Leaving the year after the journal title in a name-year reference.

In name-year, place the year immediately after the authors: “Fang FC, Steen RG, Casadevall A. 2012.” Field-specific details follow.

Related guides and tools

• Page margins and layout APA, MLA, and Chicago settings
• Citation generator APA, MLA, Chicago from a DOI or ISBN
• APA citation generator APA 7th edition
• Alphabetizer Sorts a works cited list properly
• Research essays Turning a topic into a question

Frequently asked questions