What office prepares the federal budget, what process does it follow?

Federal agencies submit their budget requests to the Executive Office of Management and Budget (OMB). The OMB prepares the budget for the President. In late fall, the OMB send revisions and notes back to the agencies, and they have until the end of the year to resubmit with changes. The OMB creates the budget based on those revisions, then submits it to the President for review in the beginning of the following year, at which time the President submits it to Congress. The process begins a year before the fiscal year for which the budget is being considered.