The chapter explores the domestic legal design of Mutual Legal Assistance (MLA) procedures, analysing individual forms of MLA such as extradition of suspects or convicts, takeover or surrender of prosecution, and execution of foreign judgments. The analysis compares legislation from three countries in Southeast Europe: Serbia, North Macedonia, and Bosnia and Herzegovina. It examines whether two key components of legal design, namely (i) the discretion granted to institutions within the criminal justice system and political establishment and (ii) the presence of checks and balances systems within MLA procedures, have a positive or negative impact on MLA policy in practice. The analysis reveals that, although the three countries share many similarities in their legal arrangements pertaining to MLA procedures, there are some variations in specific forms of MLA, in terms of the discretion granted to domestic actors and the presence of checks and balances within the procedure. The findings show that significant discretion given to specific actors within the MLA policy can pave the way for harmful practices such as arbitrariness, uneven application of the law, and potential political abuse. The study also highlights the value of incorporating built-in checks and balances within the MLA procedure to ensure accountability and mutual control mechanisms, confirming that, where such mechanisms are not present, appropriate accountability and control safeguards are missing, enabling potential abuse of power or neglect in handling the MLA procedure. At the same time, it emerges that these checks and balances, whether they include internal review mechanisms, joint decision-making models, and/or approval powers ('de facto vetoing'), should not be excessive or burdensome to avoid obstructing the MLA processes.