Where does co-citation come from?

Co-citation started in citation analysis, the study of how research papers cite each other. Wikipedia defines it as "the frequency with which two documents are cited together by other documents". The more often that happens, "the higher their co-citation strength" (Wikipedia, read 1 November 2026). Henry Small and Irina Marshakova introduced the idea in 1973, independently. Small's paper is "Co-citation in the scientific literature" (DOI).

What does co-citation mean in SEO?

SEOs borrowed the word. In SEO, co-citation usually means a page that names or links to two brands together, so search engines may learn the two are related. A list that names your product next to three well-known tools in your category is the classic case.

Be careful here: Google has not documented co-citation as a ranking signal. Its ranking systems guide talks about systems "that understand how pages link to each other", including PageRank (Google Search Central, read 1 November 2026). Whether Google also uses brands that appear together, and how, is not stated. Treat SEO claims about co-citation as practice and theory, not as Google's word.

The idea fits AI answers well. Google says AI Overviews and AI Mode may use "query fan-out", running several related searches, and can show "a wider and more diverse set of helpful links" (Google Search Central, read 1 November 2026). An assistant answering "best X" pulls from several pages and names the brands those pages name together.

Those pages are often lists. In Prefer's July 2026 check of 188 answers from ChatGPT, Perplexity, Gemini and Claude, 40% of the 1,237 citations went to independent third-party listicles. Vendors' own sites got 34%.

Our reading: if many cited lists name your product next to the category leaders, an assistant has more reason to include you in the same answer. No AI company has published this as a rule.

Why it matters for B2B SaaS

A new tool with few links can still sit in the same sentence as the leaders. That happens in a best-of list, a comparison or a forum thread. Each is a brand mention, and the company your brand keeps on the page shapes what readers and machines think it is.

Example (hypothetical)

A hypothetical new scheduling tool is named in five "best scheduling software" lists, always next to the same three market leaders. Later, a buyer asks an assistant for scheduling tools. The assistant cites two of those lists, and the new tool appears in the answer with the leaders. Nothing guarantees this. It is a pattern, not a promise.

  • A backlink is a link from one page to yours. Co-citation is about two brands on one page, with or without links.
  • A brand mention is your name on any page. Co-citation is a mention next to other named brands.
  • An AI citation is a source an assistant shows with its answer. Co-citation can describe two brands named together in that answer.

For how lists drive AI answers, see LLM SEO: how B2B SaaS brands get named in AI answers.