At the beginning of the present century, problems such as education of mentally retarded children, classification and placement of job applicants in industrial and military organizations, and students selection, gave impetus to the development of intelligence tests and the formulation of theories of intelligence. For many years factorial theories of intelligence dominated the field, but piaget's work, and later the rise of cognitive psychology, shifted the interest in the direction of cognitive lements and interpretation of intelligence. Information processing theories brought further emphasis in the same direction. In recent yeats, speed of processing has emerged as an important element in intellectual performance, and many cognitive factors have been studied from this perspective in relation to intelligence. The present paper presents an onverview of such developments in the area of general intelligence.