In today's businesses, there is a trend that service-oriented architecture (SOA) is evolving into a popular architectural paradigm for IT infrastructure. SOA allows companies' software systems to be shared as network-enabled electronic services with their commonly specified interfaces. Service discovery and composition are two emerging ones which are both fundamental and important to SOA. Service discovery occurs when software modules identify suitable services that meet pre-established requirements based on the service descriptions. Service composition takes one step further to chain up the discovered services as execution plans. To motivate and promote the research in the areas, the Web Services Challenge 2006 (WSC-06) is organized and will take place at the joint 2006 CEC/EEE conferences. Building upon the success of the first two Web Services Challenges held at EEE-05 and ICEBE-05, WSC-06 contains new challenges that consider not only exact match, but also subsumption relations between input and output types, thus simulating semantic search. The competition solicits academic and industry researchers to develop software systems for discovering Web services and also composing them to create higher-level capabilities.