A great deal of learning occurs in contexts where people can regulate their study and hence can control their success. College students may decide to focus on mastering some class materials and to largely ignore others; on the job, doctors may decide how much time to devote to learning about the new advances in their field; and for a hobby like bird watching, an enthusiast can choose how to allocate their time to learning birds' names and their songs. Thus, people's success at learning will be driven in part by how they allocate their study time, which brings us to the main question of this chapter: What drives people's allocation of study time as they are attempting to learn new materials? This question has received much attention since Rose Zack's seminal research in 1961, so to put our current answer in context, we first briefly describe some of the earliest empirical and theoretical work on study-time allocation.