Pervasive computing is all about making information, data and services available everywhere and anytime. The explosion of huge amounts of data largely distributed and produced by different means (sensors, devices, networks, analysis processes, more generally data services) and the requirements to have queries processed on the right information, at the right place, at the right time has lead to new research challenges for querying. For example, query processing can be done, locally in the car, on PDA or mobile phone or it can be delegated to a distant server accessible through Internet. Data and services can therefore be queried and managed by stationary or nomad devices, using different networks. The main objective of this chapter is to present a general overview of existing approaches on query processing and our vision on query evaluation in pervasive environments. It illustrates, with scenarios and practical examples, existing data and streams querying systems in pervasive environments. It describes the evaluation process of (i) mobile queries and queries on moving objects, (ii) continuous queries and (iii) stream queries. Finally, the chapter introduces our vision of query processing as a service composition in pervasive environments.