Direct Answer
The MSCI World IMI is a rule-based measurement of large-, mid-, and small-cap equities across 23 developed market countries worldwide, maintained by MSCI. Like every index it owns nothing: it is a number produced by applying a published weighting formula to a selected list of companies, revised on a schedule the provider sets.
What this index covers
The MSCI World IMI covers large-, mid-, and small-cap equities across 23 developed market countries worldwide, within the Global market. MSCI defines which securities are eligible, how they are selected from that pool, and how much each one contributes to the published number.
The index name does not state a fixed company count, so the number of constituents follows the eligibility rules rather than a target.
How constituents are weighted
Free float-adjusted market capitalization weighting applies to large, mid and small cap constituents alike. The index is the developed markets composite of each market's Investable Market Index, so small caps are weighted by float-adjusted size inside the same index.
The weighting method is the single biggest driver of how an index behaves. Two indexes covering the same market can diverge for years purely because they weight differently, which is why comparing index levels without knowing the method tells you very little.
What qualifies for inclusion
It combines the Investable Market Index of every developed market, which is the Standard Index plus the Small Cap Index, targeting 99% of free float-adjusted market cap in each market (plus 1% or minus 0.5%). A security needs float-adjusted market cap of at least 50% of the market's IMI size cutoff, bounded by the global minimum size range, plus the standard developed market foreign inclusion and liquidity screens.
Eligibility rules are the part of an index most readers never look at and the part that decides what it can possibly measure. A screen that excludes a whole sector, or admits only one listing venue, shapes the result far more than any day of trading does.
How long a listing must exist first
A new issue must have started trading at least three months before the implementation of an Index Review to be eligible. Significantly large IPOs and large offerings by non-constituents are exempt from the three month rule, and significantly large IPOs may be added after the close of their tenth trading day.
A seasoning rule is why a large new listing does not appear in an index the week it starts trading. It is a deliberate lag, and it means an index can under-represent a fast-growing part of the market for months at a time.
When the membership is revised
Index Reviews are quarterly, in February, May, August and November, and each one is a full reassessment of the equity universe, size cutoffs, buffer zones, foreign inclusion factors and share counts. Results are announced at least two weeks ahead and generally take effect at the close of the last business day of the review month. A Small Cap Entry Buffer of 1.5 times the IMI cutoff limits how many new small caps enter at once.
Reconstitution is the one date an index changes shape by design rather than by price. Funds tracking it have to trade toward the new membership, which is why the schedule matters to anyone holding the tracker rather than only to the provider.
The rule that surprises people
The Small Cap segment is defined as the difference between the IMI and the Standard Index, so it never overlaps with large or mid caps. A non-constituent small cap inside the entry buffer joins only to the extent it replaces a constituent that fell below the lower buffer.
References
- MSCI: MSCI, MSCI GIMI Methodology: Index Construction Objectives, Guiding Principles and Methodology for the MSCI Global Investable Market Indexes, as published 2026. Every rule described on this page is taken from this document.
Current MSCI World IMI constituents
MSCI publishes and licenses the MSCI World IMI constituent list. Swoopr does not republish it here. The provider's own page is the authoritative source for current membership and weights.
Related reading
- All stock market indexes: how indexes are built, weighted and revised.
- Global indexes: others covering the same region.
- Index concentration: measuring how much of an index sits in its largest holdings.
- Index rebalancing and inclusion effects: what happens to a stock when index membership changes.
Frequently Asked Questions
Who maintains the MSCI World IMI?
MSCI maintains the MSCI World IMI and publishes the methodology document that defines its eligibility and weighting rules.
What does the MSCI World IMI measure?
It measures large-, mid-, and small-cap equities across 23 developed market countries worldwide. The index is a calculated number applying a weighting formula to a selected list of companies, and it holds nothing itself.
Where can I see the current MSCI World IMI constituents?
MSCI publishes the current constituent list. Swoopr does not republish it, because index providers license constituent data and Swoopr holds no such licence.