This chapter discusses language, cognition, problem solving, and decision making. It explains that cognition involves thinking and meta-cognition is thinking about thinking. Adolescents develop new cognitive skills like meta-cognition. The chapter also discusses how people differ in their need for cognition, with some enjoying cognitive puzzles more than others. It explores how people learn language from a young age and problem solving strategies like preferring known options for some decisions and weighing unknowns for risky decisions.