The index includes a collection of stocks of all the developed markets in the world, as defined by MSCI. The index includes securities from 23 countries but excludes stocks from emerging and frontier economies making it less worldwide than the name suggests. A related index, the MSCI All Country World Index (ACWI), incorporated both developed and emerging countries. MSCI also produces a Frontier Markets index, including another 31 markets. The MSCI ACWI Index, MSCI’s flagship global equity index, is designed to represent performance of the full opportunity set of large- and mid-cap stocks across 23 developed and 26 emerging markets. As of December 2019, it covers more than 3,000 constituents across 11 sectors and approximately 85% of the free float-adjusted market MSCI USA: The MSCI USA Index represents 63% of the MSCI World Index 1. It is designed to measure the performance of the large and mid-cap segments and aims to represent ~85% of the US market. It is designed to measure the performance of the large and mid-cap segments and aims to represent ~85% of the US market.