This document discusses theories and research on the nature and measurement of intelligence. It begins by asking the reader to consider their own definition of intelligence and noting there is no single agreed upon definition. It then reviews several theories of intelligence, including psychometric theories that view intelligence as a single general factor (g) or combination of general and specific factors, Gardner's theory of multiple intelligences, and Cattell's fluid and crystallized intelligence. The document also examines methods of measuring intelligence, including early IQ tests and more modern tests like the Stanford-Binet and WAIS/WISC. Finally, it reviews research on factors that can influence measured intelligence such as genetics, environment, poverty, gender, race/ethnicity and