What is SOA?
Service oriented architecture (SOA) is an architectural style for integration. SOA uses an integrated software infrastructure and design approach based on best practices in order to decompose monolithic architectures into shared and reusable business services.

What are Web services?
Based on open standards, Web services allow computer programs to exchange information over the Internet by eliminating the incompatibility created by disparate hardware platforms, software languages, and operating systems.

How does SOA leverage Web services?
Because they are based on open standards, Web services are playing out to be the technology of choice for SOA. Most IT departments cite the need to integrate disparate systems as the main reason they consider implementing Web services. Unlike Web services, however, SOA is more than a flavor of the month from a particular vendor; SOA represents a seismic shift in the way businesses architect, deploy, and manage information technology.