Developing a budget for a grant proposal is similar to writing other sections of the application. It takes time, careful thought, knowledge of technical budget terms, and an understanding of the budgetary requirements and restrictions of both the funding agency and the investigator’s institution. It is important to begin developing a budget for a proposal as early as possible in the grantwriting process. As soon as the investigator has identified a project idea and its specific aims, they should consider the budget to ensure that the proposal idea and aims are realistic from a funding perspective. This chapter helps the reader understand the language of grant budgets, consider the policies and requirements of both the agency and the reader’s institution, identify the components of a budget, write a budget justification, and determine when to use the National Institutes of Health (NIH) modular budget format.