This chapter reviews the history of artificial intelligence (AI) and its major subfields, and illustrates AI as a science and as a technology. Critics of AI from psychology sometimes view AI programs as being psychologically implausible. The chapter explains some dimensions in designing AI agents as well as describes some issues in putting multiple capabilities into an AI agent. It discusses the problems of the measurement of intelligence in AIs. When measuring the intelligence of human beings, the test need not have questions representing every kind of intelligent thing a person could do. Rather, the test result measures the general intelligence of the test taker. A lesson from the history of AI is that cognitive tasks that seem difficult for humans to solve are relatively easy to make programs solve, and those cognitive tasks that are apparently easy for humans to address are extraordinarily difficult to make computers solve.