The development of content knowledge is essential for interest development and is also an outcome of interest development. This chapter provides a context for thinking about declines in interest. It considers how interest is related to content knowledge as well as the relation between interest and identity. The chapter explores the meaning of interest-driven learning and explains that interest can be supported to develop in a variety of settings. It reviews some findings from studies of interest conducted both in and out of school, organized by subject matter, or domain: reading, writing, second-language learning, history, science, mathematics, art, music, and physical education. Interest can be triggered and supported to develop both in and out of school, and advanced training in a sport, music, art, drama, or writing is an example of interest-driven learning that when undertaken outside of school can complement, provide enrichment, or even be a replacement for schooling.