While several peer-to-peer (p2p) schemes have emerged for distributed data storage, there has also been a growing undercurrent towards the invention of design methodologies underlying these peer-to-peer systems. A design methodology is a systematic technique that helps us to not only design and create new p2p systems (e.g., for data storage) in a quick and predictable manner, but also increases our understanding of existing systems. This chapter brings together in one place previous and existing work by several authors on design methodologies that are intended to augment the activity of p2p algorithms, keeping our focus centered around (but not restricted to) data storage systems. As design methodologies grow in number and in power, researchers are increasingly likely to rely on them to design new p2p systems.