The national horseracing federations of the countries bordering the Mediterranean Sea and/or the Black Sea and/or the racing clubs organisers of any leg of the Mediterranean Championship can become members of the Union.
The Mediterranean Horseracing Union is the first supranational organisation joining together the two sectors of gallop and trot. Therefore, since there are countries where the two disciplines are represented by diverse federations, some countries adhere to the Union with two different federations.

The constitution of this Association followed a route similar to the one that brought to the sealing of the Declaration of Barcelona for the creation of the Mediterranean free-trade area in 2010. Also in that case the participating countries arrived to the conclusion of recognising the cultural and commercial relationship heritage among the people as the common denominator to identify the countries to involve in the project. The Euro-mediterranean partnership was therefore enlarged to invclude other countries not directly bordering with the Mediterranean sea, like Portugal and Serbia, as well as to the Black Sea area.