The EMBI (Emerging Market Bond Index) is JP Morgan's index of dollar-denominated sovereign bonds issued by a selection of emerging market countries. 
The family of EMBI is the most widely used and comprehensive emerging market sovereign debt benchmark. In addition to serving as a benchmark to measure the performance of the asset class, the indices define and increase the visibility of the emerging market sovereign debt market and provide a list of the instruments traded along with a compilation of their terms.
There are three different EMBI indices produced by J.P. Morgan's Global Index Research group: EMBI+, EMBI Global, and EMBI Global Diversified. The indices are rule-based with specific liquidity, maturity and structural constraints.
Emerging Markets Bond Index Plus (EMBI+): This tracks total returns for traded external debt instruments (external meaning foreign currency denominated fixed income) in the emerging markets. EMBI+ covers US dollar-denominated Brady bonds, loans and Eurobonds.
The EMBI+ expands upon J.P.Morgan's original Emerging Markets Bond Index (EMBI), which was introduced in 1992 and covered only Brady bonds. Instruments in the EMBI+ must have a minimum face value outstanding of $500 million and must meet strict criteria for secondary market trading liquidity.
EMBI Global: The J.P.Morgan Emerging Markets Bond Index Global ("EMBI Global") tracks total returns for traded external debt instruments in the emerging markets, and is an expanded version of the EMBI+. As with the EMBI+, the EMBI Global includes US dollar-denominated Brady bonds, loans, and Eurobonds with an outstanding face value of at least $500 million.
However, instead of selecting countries according to a sovereign credit-rating level (as it is done with EMBI+), the EMBI Global defines emerging markets countries with a combination of World Bank-defined per capita income brackets and each country's debt-restructuring history. These two criteria allow the EMBI global to include a number of higher-rated countries. Also, EMBI Global's secondary market liquidity constraints are much more relaxed than EMBI+, and results in inclusion of nearly twice as many instruments than the EMBI+.
EMBI Global Diversified: This limits the weights of countries with larger debt stocks by only including a specified portion of these countries' eligible current face amounts of debt outstanding.
The EMBI family of indices was launched in the summer of 1999 and historical daily data has been backfilled to December 1993.
In July of 1999, the three largest constituents of the EMBI Global were Argentina 20.4%, Brazil 19.2% and Mexico, 15.2%. On December 31, 2010, the three largest constituents were Mexico, 11.84%; Russia, 11.60% and Brazil, 10.44%. Argentina represented only 2.08% of the 2010 capitalization.