This chapter explores that complexity. It begins with an overview section that assumes that the ultimate aim of any military manpower management process is to have in place a force structure that is appropriate to a nation’s security needs. From that it follows that the management process has to be a kind of quasi-market mechanism, one that attempts to match the supply of military manpower to the demand for it. On the demand side, the challenge is to know just what manpower numbers and mix of skills are required. These have to be determined within some form of force planning process that considers manpower requirements simultaneously with decisions regarding equipment, doctrine and organisation. But ultimately, the demand for military manpower will be driven by four critical considerations: the state of the international security environment; the perceived utility of military force in that environment; the technology of warfighting; and, as always, by issues of affordability. These factors and their implications for manpower requirements are discussed in the third and fourth sections of this chapter. On the supply side, the challenge is to manage a lifecycle process of recruiting, training, promoting, deploying and finally releasing the right numbers of individuals such that there is a dynamic synchronisation of the distribution of available numbers and skills with the distribution of numbers and skills actually required to support the force structure. The fifth section of this chapter examines this process in detail. In particular, it addresses the issues that manpower managers face as they attempt to manage what is generally quite an inflexible process in the face of shifting demographics and changing labour markets. The sixth section explores some ideas for dealing with these issues through changing manpower supply processes to make them more flexible and hence more responsive to military requirements. A concluding section summarises the need for manpower management change and reflects on the factors that will determine how far and how fast that change might go.