This chapter covers the perceptron, the simplest neural network architecture. In general, neural networks are machine learning architectures loosely inspired by the structure of biological brains. The perceptron is the simplest example of such architectures: it contains a single artificial neuron. The perceptron will form the building block for the more complicated architectures discussed later in the book. However, rather than starting directly with the discussion of this algorithm, we will start with something simpler: a children’s book and some fundamental observations about machine learning. From these, we will formalize our first machine learning algorithm, the perceptron.