To find significant patterns, we will first calculate the number of appearances of different patterns in real and random networks. We will focus in this chapter on patterns with three nodes (such as triangles). There are 13 possible three-node patterns (Figure 4.1). Patterns with two nodes and patterns with more than three nodes will be discussed in the next chapters. We will see that of the 13 possible three-node patterns, only one, the feed-forward loop (FFL), is a network motif.