In this chapter we look at fundamental concepts in machine learning and how these apply in the context of medical image analysis. We consider both classical approaches, as well as the increasingly widely used artificial neural network, and even more recently developed ‘deep learning’ approaches with attention paid to machine learning architectures that are specially suited to imaging data. This serves as an introduction and reference for a range of methods that are widely used in image analysis (Chap. 14 ) and automated medical image interpretation.