Web of Science is a curated, selective citation-indexing platform operated by Clarivate that records scholarly publications and the citation links between them, enabling researchers to trace how ideas connect across the literature. Rather than indexing everything it can find, Web of Science applies editorial selection criteria, and its data underpins widely used research metrics including those published in the Journal Citation Reports.
This article explains what the Web of Science Core Collection contains, how citation indexing works, its relationship to the Journal Impact Factor, and why a citation index is fundamentally different from a general search engine.
The Core Collection and selective indexing
At the heart of Web of Science is the Core Collection, a set of citation indexes covering the sciences, social sciences and arts and humanities, together with conference proceedings and book content. The defining characteristic is selectivity: journals are evaluated against editorial and quality criteria before being accepted, and coverage is curated rather than exhaustive. The intention is that the corpus represents influential, well-edited scholarly literature, so that the citation relationships drawn from it are meaningful.
This selectivity is the central trade-off of the platform. A narrower, vetted corpus yields cleaner citation data, but it also means many legitimate outputs — particularly in regions, languages or fields with less established journals — may fall outside coverage. Understanding what is and is not indexed is essential before using the data for any kind of assessment.
The citation index: Garfield’s idea
The conceptual foundation of Web of Science is the citation index, an idea developed by Eugene Garfield, who founded the Institute for Scientific Information. The insight was simple but powerful: by systematically recording which papers cite which other papers, you create a navigable network of the literature. From any article you can move backwards to the references it cites and forwards to the later papers that cite it.
This forward-and-backward navigation is what distinguishes a citation index from a bibliographic list. It lets researchers follow the development of an idea over time, identify foundational works, and gauge the influence of a paper by the citations it accrues. The same citation graph is the raw material from which bibliometric indicators are computed.
The Journal Citation Reports and the Impact Factor
Web of Science citation data feeds the Journal Citation Reports (JCR), Clarivate’s annual analysis of journal-level citation performance. The JCR is the source of the well-known Journal Impact Factor, a journal-level metric calculated from citation counts to a journal’s recent articles. Because the Impact Factor is derived from Web of Science data, a journal must be indexed in the relevant part of the Core Collection to receive one.
| Element | What it is |
|---|---|
| Core Collection | The curated set of citation indexes underpinning the platform |
| Citation index | The network of citing–cited relationships between publications |
| Journal Citation Reports | Annual journal-level citation analysis built on the data |
| Journal Impact Factor | A journal-level metric published within the JCR |
It is important to stress that the Impact Factor is a journal-level measure and is widely cautioned against as a proxy for the quality of any individual article or researcher. Responsible-metrics initiatives encourage using it carefully and in context.
How it differs from a search engine
A general web search engine indexes pages it can crawl and ranks them by relevance and popularity signals. Web of Science is different in three respects: its corpus is selected rather than crawled; its core data structure is the citation graph rather than full-text relevance; and its records are structured bibliographic metadata — authors, affiliations, references, funding — rather than raw web content. This makes it a tool for analysis and discovery within the scholarly record, not a general-purpose finder of web pages. Related tools and systems are covered across our research information systems section.
Web of Science is frequently compared with Elsevier’s Scopus, the other large multidisciplinary citation database; we set the two side by side in our Scopus versus Web of Science comparison. Both rely on persistent identifiers such as the DOI to link records reliably, and definitions of the metrics involved appear in the CASRAI dictionary.
Frequently asked questions
Is Web of Science free to use?
No. Web of Science is a subscription product from Clarivate, typically licensed by universities, research institutions and libraries. Access depends on your organisation’s subscription.
Does being in Web of Science mean a journal is high quality?
Inclusion signals that a journal met the platform’s selection criteria, which is a meaningful editorial threshold. It is not, however, an absolute or universal measure of quality, and many reputable journals sit outside its coverage.
What is the difference between Web of Science and the Journal Citation Reports?
Web of Science is the underlying citation database; the Journal Citation Reports is an annual analytical product built from that data, and it is where the Journal Impact Factor is published.
Who invented the citation index?
The citation-index concept was developed by Eugene Garfield, founder of the Institute for Scientific Information, whose work established the systematic recording of citation links that Web of Science still embodies.
