This chapter reviews the role of the Mexican legislature in the budget process. Over the past decade, the Mexican Chamber of Deputies has become a much more active participant in the budget process. This development reflects the changes in the political system and the nature of the legislative-executive relationship. On a number of occasions, the budget process has become the focal point of conflict between the two branches. Recent reforms to the legislative budget process have provided tools to strengthen legislative oversight and have helped to some extent to clarify the respective roles of the legislature and the executive. Combined with a growing cross-party willingness to co-operate on the budget and greater emphasis on fiscal responsibility, the legislative budget process has been greatly improved.