With more and more availability of services, Web service composition (WSC) based SOA implementations have increasingly become a significant type of SOA projects in practice. However, effort estimation for such a type of SOA project can still be limited because of the numerous and various approaches to WSC. In other words, it is impossible to collect development data through experiments to do quantitative effort estimation for WSC-based SOA implementations. Through viewing WSC-based SOA system from a perspective of mechanistic organization, this book borrows Divide-and-Conquer (D&C) as the generic strategy to narrow down the problem of effort judgment for the entire SOA implementation to that for individual WSCs. As such, this book reveals an initial and qualitative step toward effort judgment for SOA implementations.