This chapter introduces association rule learning, a machine learning topic that could appear much different from others. Thus, to flatten the learning curve, we will first go through the definition, data format, scope, and history of association rule learning using language that can be easily understood. Next, essential concepts of association rules will be laid down in a more technical way to provide the knowledge needed for understanding representative algorithms. Based on that, three popular association rule learning algorithms, i.e., Apriori, FP Growth, and Eclat, will be explained. The procedures of performing association rule learning using these three algorithms will be detailed as we work through a typical problem using each of them.