The Markets in Financial Instruments Directive (Mifid), launched in November 2007, is the European initiative to promote competition and enhance choice for investors across Europe.
It requires brokers to achieve “best execution” for their clients - typically so-called “buyside” investors like asset managers.
This means brokers and dealers are obliged to obtain the best possible result of a trade for a client, taking into account not just price but costs, speed, likelihood of execution and settlement, size, and other considerations.
However, Mifid never spelled out how to achieve best execution. The result is that brokers write their own best execution policies, which may differ from one to another.