In this chapter, we set out to describe the fundamental requirements, objectives and process for an effective and efficient maintenance program or policy. This is achieved though reference to and analysis of the literature as well as the results of our own research. We explore the difficulties and complexities in determining such a policy in practice arriving at recommendations on practical approaches to its development. This provides context for what might be termed mathematical approaches to determining such aspects of these policies as the frequency of a proposed action and the resulting cost and reliability to be expected if they are applied to the item under study. Challenges in applying such analytical tools include the nature of available data and the complexity of the overall decision process directed at whole of life, multifactorial, whole system outcomes.