The Climate Modelling Toolkit (CliMT) is a Python-based software component toolkit providing a flexible problem-solving environment for climate science problems. It aims to simplify the development of models of complexity ’appropriate’ to the scientific question at hand. This aim is achieved by providing Python-level access to components commonly used in climate models (such as radiative transfer models and dynamical cores) and using the expressive data structures available in Python to access and combine these components. This paper describes the motivation behind developing CliMT, and serves as an introduction to interested users and developers.