A container is an object holding objects. Arrays are one of the two most widely used POOMA containers since they model the mathematical concept of mapping from domain indices to values. POOMA Arrays extend built-in C++ arrays by supporting a wider variety of domains, automatically handling memory allocation, and having first-class status. For example, they may be used as operands and in assignments. In this chapter, we introduce the concept of containers, the mathematical concept of arrays, and the POOMA implementation of Arrays. Before illustrating how to declare Arrays, we introduce Domains, which specify the sets of indices. After describing how to declare the various types of Domains, we describe how to declare and use Arrays.