Budgeting for national defense is a complex endeavor, particularly for a nation like the U.S. that assumes global responsibility and strives to have the most advanced and lethal force on earth. It is necessary – and challenging – to balance the myriad requirements between current and future readiness, across warfare areas and military services, between having state of the art capability with sufficient capacity, and among people, hardware, and the activities people do with that hardware. As analytically difficult as that problem is, it is embedded in the political budgeting processes and national security must be balanced with every other function of government and there must also be cooperation across branches of government. This text explores that complex endeavor. It takes the position that budgeting for defense is a particular instance of public budgeting which is a particular instance of public policy. Thus, this text starts with a conceptual, empirical, and process foundation before discussing the participants and processes that build the annual defense budget. It then covers the execution of that budget and the ultimate accounting. Compared to the first edition, this text is updated with current figures and examples. There is a new chapter on determinants of military spending in society and burden sharing within alliances. The chapter on budget execution has been disaggregated and a new chapter is devoted to fiscal law. The final chapter seeks to integrate all that came before it by discussing matters that integrate the stages of budgeting and which cross branches of government. Following in the tradition of the first edition, this is intended to be both a textbook for a course in budgeting, but also a desktop reference for defense budgeting practitioners.