This chapter reviews classic theories of CMC that are relevant to understanding personal media use, including media richness theory, social presence theory, channel expansion theory, the hyperpersonal model, social information processing theory, channel complementary theory, and media multiplexity theory. The chapter also explores emergent and important perspectives, such as relationship interdependence and mundane mediated relationship maintenance. This chapter introduces the communicate bond belong (CBB) theory, which examines how the content of communication, particularly the episode of communication, influences the satiation of the fundamental need to belong. One advantage of CBB is its focus on human energy management, which stipulates that humans seek to conserve energy expenditure and invest their time and energy toward future belongingness need satiation. From the perspective of CBB theory, personal media use is understood as result of three forces: need satiation, energy conservation and investment, and homeostatic balance of social interaction and time alone.