Volunteer Computing (VC) and Desktop Grids (DGs) collect and make available the donated resources from non-dedicated computers like office and home desktops. VC and DG paradigms seem similar, however they target different use cases and environments: DG systems operate within the boundaries of institutes, while VC collects resources from the public internet. VC systems are usually deployed to solve a grand compute intensive problem by researchers who either don't have access to or don't have the resources to use a dedicated infrastructure, or simply don't want to maintain such an infrastructure. Although there are informal attempts to categorize systems and formal models derived from existing systems, there is no formal definition for the relationship between DG and VC. This book makes an attempt to formalize VC and DGs, their relationship, and evaluate existing systems. Next, starting from a definition for Cloud Computing, the required steps are identified and a definition formulated for what can be considered as the next evolutionary stage for VC: Volunteer Clouds. Finally, several improvements are proposed that allow narrowing the gap between VC and Volunteer Clouds.