In this paper we present a toolkit for realizing capacitive sensing applications for human-computer interaction in pervasive computing systems. We argue that capacitive sensors - due to their unique properties - are well suited for many pervasive and ubiquitous computing applications and scenarios. We describe the CapToolKit designed to rapidly realize prototypes and systems that are able to detect the presence of humans and objects. Our toolkit also allows the integration of 3D interaction with everyday objects as well as instrumented environments. We illustrate its capabilities by presenting several applications implemented using Cap- ToolKit. The entire system will be open-sourced to allow utilization of our technology within other research projects. By building on the existing toolkit researchers are provided a foundation for developing their own sensor systems, algorithms, and applications.