A mutual legal assistance treaty is an agreement between two countries for the purpose of gathering and exchanging information in an effort to enforce public laws or criminal laws. First ones are very important in tax matters, in particular as part of international double taxation agreements wherein the parties agree to deliver information for tax purposes.
This assistance may take the form of examining and identifying people, places and things, custodial transfers, and providing assistance with the immobilization of the instruments of criminal activity. With regards to the latter, MLATs between the United States and Caribbean nations do not cover U.S. tax evasion, and are therefore ineffective when applied to Caribbean countries, which usually act as offshore "tax havens." [1]
Assistance may be denied by either country (according to agreement details) for political or security reasons, or if the criminal offence in question is not equally punishable in both countries. Some treaties may encourage assistance with legal aid for nationals in other countries.