The review on research on basic memory capacities and working memory presented in this chapter indicates that the area has been very active since the early 1980s. On the one hand, this is certainly related to the fact that theoretical models such as those developed by Baddeley, Case, Cowan, and Pascual-Leone have attracted a lot of attention and have stimulated empirical research to test basic assumptions. On the other hand, this research has also demonstrated that the concept of working memory is not only relevant to the memory domain but also has important implications for other research areas. That is, the ability to hold small amounts of information in a temporary store and to act on that information for the purpose of solving problems is central to many areas of cognition and foundational to the execution of many cognitive tasks. The capacity of a person's working memory puts limits on the type of higher-order cognitive operations one can perform. Although it is still unknown why developmental growth in working memory capacity occurs, there is reason to assume that different factors such as brain growth, knowledge increases and strategy acquisition, developmental changes in information processing speed, and rates of memory trace decay all contribute to the developmental process.