Artificial neural networks are special functions inspired by brains. In particular, artificial neural networks consist of interacting (artificial) neurons that model biological neurons (nerve cells). Modern artificial neural networks comprise hundreds, thousands, or even millions of neurons organized in multiple layers. Machine learning based on such networks is called deep learning. This chapter introduces the basic principles of artificial neural networks and deep learning. You learn to – assemble individual neurons into networks; – use these networks for binary and multiclass classification; – assess the potential and limitations of deep learning.