Web of Science

What Web of Science is

Web of Science is a citation-indexing and research-discovery platform owned and operated by Clarivate — not a single index and not a journal list in its own right. Searching Web of Science means searching across a bundle of separately curated citation indices that Clarivate hosts on one platform, each with its own editorial-selection criteria and scope. In practice this means a claim that a journal is “in Web of Science” is only precise once it names which underlying index accepted it — most often the Science Citation Index Expanded (SCI/SCIE), but Web of Science also spans the Social Sciences Citation Index, the Arts & Humanities Citation Index, and the regional and specialty indices described below.

Platform structure: the Core Collection, plus regional and specialty indices

The Web of Science Core Collection is the platform’s central bundle of six citation indices:

• Science Citation Index Expanded (SCIE) — sciences, with backfile coverage to 1900
• Social Sciences Citation Index (SSCI) — social sciences, with backfile coverage to 1900
• Arts & Humanities Citation Index (AHCI) — arts and humanities
• Emerging Sources Citation Index (ESCI) — journals under evaluation that don’t yet meet full SCIE/SSCI/AHCI criteria
• Conference Proceedings Citation Index (CPCI) — indexed conference literature
• Book Citation Index (BCI) — scholarly books

Beyond the Core Collection, Clarivate has progressively added regional citation indices to the same platform, extending coverage into scholarship the Core Collection’s selection criteria have historically underrepresented: the Chinese Science Citation Database (added 2008, produced with the Chinese Academy of Sciences), the SciELO Citation Index (2013, covering Brazil and other Latin American countries, Spain, Portugal, the Caribbean, and South Africa), the Korea Citation Index (2014), the Russian Science Citation Index (2015), and the Arabic Citation Index (2020, launched with the Egyptian Knowledge Bank). The platform also carries specialty databases layered on top of these — including BIOSIS, Zoological Record, the Data Citation Index, and the Preprint Citation Index — and, for many subscribing institutions, MEDLINE search within the same interface. A given institution’s actual Web of Science access varies with which of these indices its license covers, so “covered by Web of Science” is not one fixed scope across every subscriber.

Why “indexed in Web of Science” is an ambiguous claim

Because the Core Collection is a bundle rather than a single list, “indexed in Web of Science” names a family of statuses rather than one status. The precise question — and the one a promotion committee, a national research-assessment exercise or a funder eligibility rule is usually actually asking — is which index the record sits in. For a journal, Clarivate’s free Master Journal List settles it: the journal profile page names the index (SCIE, SSCI, AHCI or ESCI) and the coverage start year. Inside a Web of Science session, the same information appears on the record’s full view and in the Editions selector that governed the search you just ran.

One caveat on the enumeration above: Clarivate’s current public Core Collection page lists these six indexes and no others (checked 26 August 2026). Older Web of Science interfaces additionally exposed two chemistry indexes — Current Chemical Reactions and Index Chemicus — as separately licensable Core Collection editions. CASRAI could not confirm their current status from Clarivate’s own Core Collection page, and Clarivate’s detailed product documentation sits behind institutional authentication, so this page does not assert either way. Your own Editions selector is authoritative for what your subscription includes.

ESCI is inside the Core Collection but is not treated like the rest of it

ESCI is a genuine Core Collection index, so a journal covered only by ESCI is accurately described as Core Collection-indexed. It is nevertheless the index most often carved out of assessment rules: institutional promotion criteria, national assessment exercises and funder publication-eligibility conditions frequently name SCIE, SSCI and AHCI specifically, or say “Web of Science Core Collection” and then qualify it — because ESCI is designed as the entry tier for journals that meet Clarivate’s baseline editorial-quality criteria but have not been accepted into the older, more selective indexes. Where an eligibility rule is load-bearing, read the rule’s own wording rather than inferring its scope from the phrase “Core Collection”.

What changed in 2023, and why it changes how a JIF should be read. Through the 2022 Journal Citation Reports release, only SCIE- and SSCI-indexed journals received a Journal Impact Factor. Starting with the 2023 JCR release, Clarivate extended JIF eligibility to all Web of Science Core Collection journals meeting its quality criteria, including AHCI and ESCI titles — more than 9,000 journals received a JIF for the first time in that release. The consequence is narrow and easy to miss: since 2023, “this journal has a Journal Impact Factor” no longer implies SCIE or SSCI membership, so a JIF cannot be used as a proxy for which index a journal sits in. Check the index itself. Separately, from the 2024 JCR release Clarivate ranks arts and humanities categories by the Journal Citation Indicator rather than by JIF.

Your institution’s subscription decides which corpus you actually search

A Web of Science subscription is licensed by edition and by backfile depth, not as one undifferentiated product. Which of the Core Collection indexes appear in your Editions selector, and how far back each one reaches, is a property of your institution’s licence. Two researchers at two universities running an identical query against “Web of Science” can therefore be searching materially different corpora, and can get different result sets, different citation counts and different derived metrics from them. It is the single most practical thing to know about the platform and it is almost never stated.

The operational rule that follows: before recording or reporting any Web of Science figure, note which editions and which year range the session actually covered, and record them alongside the number. A librarian can confirm the institution’s entitlement in a minute. This is also why a Web of Science h-index is not purely a property of a publication record — that guide sets out the subscription-dependency mechanism and the wider coverage differences between Web of Science, Scopus and Google Scholar in detail.

From “Web of Knowledge” to “Web of Science”

The platform’s current name is more recent than the underlying index. The online successor to the print Science Citation Index launched in 2002 as ISI Web of Knowledge, under the Institute for Scientific Information / Thomson Corporation. After Thomson Corporation and Reuters merged in 2008, the platform continued under “Thomson Reuters Web of Knowledge” branding. Thomson Reuters renamed the platform Web of Science in January 2014 — the name it has carried since, through the 2016 spin-out and sale of Thomson Reuters’ Intellectual Property & Science business (rebranded Clarivate Analytics, now Clarivate) that made Clarivate the platform’s current owner and operator. A citation, library guide, or older paper that refers to “Web of Knowledge” is describing the same underlying platform under its pre-2014 name, not a different product.

Web of Science vs. the indices within it

“Web of Science” and “Science Citation Index” are related but not interchangeable terms. The Science Citation Index / SCI Expanded is one citation index — the platform’s oldest and largest — that sits inside the Web of Science Core Collection; it is a component of the platform, not a synonym for it. A journal can accurately be described as “Web of Science-indexed” while covered only by a regional or specialty index, without ever having been evaluated for SCIE at all (see the worked examples in the sidebar).

Web of Science vs. Scopus and OpenAlex

Web of Science is one of several competing citation databases researchers, librarians, and research offices use for literature discovery and bibliometric analysis — most often compared against Elsevier’s Scopus and the open, non-proprietary OpenAlex. The three differ in ownership, journal-selection criteria, coverage, and the citation metrics each one calculates (Web of Science underlies the Journal Impact Factor via Journal Citation Reports; Scopus underlies CiteScore). For a detailed side-by-side comparison of coverage, cost, and metrics, see Scopus vs Web of Science vs OpenAlex: Comparing Bibliographic Databases.