This book is intended for software developers who have some experience with machine learning. scikit-learn's API is well-documented, but assumes that the reader understands how machine learning algorithms work and when it is appropriate to use them. This book does not attempt to reproduce the API's documentation. Instead, it describes how machine learning models work, how their parameters are learned, and how they can be evaluated. When practical, we will work through toy examples of the algorithms in detail to build the understanding required to apply them effectively.