Theories of adult learning can be studied from individual, social, and cultural perspectives. The individual viewpoint has dominantly focused on cognitive aspects, dating back to the ancient philosophers who set the grounding for our understanding of human knowledge production. Today, a well-developed understanding of adult learning processes considers learning as a complex system where learning processes on different levels interact but are not reducible to each other. The roles of memory, executive functions, and deliberate practice are elaborated in this chapter. Motivational, metacognitive, and regulation aspects have added to our understanding of the success of individual learning processes, complemented with the more recent notions of the importance of different types of conceptions and changes in them. Looking at learning processes from social and cultural perspectives have helped us to understand the situational and collaborative nature of knowledge building processes. In adult learning situations, such as in studying or working life contexts, the individual and social learning are intertwined, making use of participants prior understanding and resulting in collaborative knowledge building.