Quantum machine learning is a subject in the making, with endless possibilities for applications in the near and long term. Nonetheless, to find out what quantum machine learning has to offer its numerous possible avenues first have to be explored by an interdisciplinary community of scientists and quantum computing enthusiasts. This book in intended to be a starting point for this journey, as it to introduces key concepts, ideas, and algorithms that are the result of the first few years of quantum machine learning research.