A system is context-aware if it uses context to provide relevant information or services to the user, where relevancy depends on the user’s task. Context-awareness is offering services to users with react of proactively to user environment and service conditions. The main goal of context-aware system is to track and identify the users. There exist many approaches for modeling context information and each model brings along some reasoning techniques. Many researchers are concentrated the context aware computing and pervasive computing and has developed different context modeling and reasoning techniques. This paper mainly addresses key performance issues, challenges and different modeling techniques for Context aware computing and summarizes them.