This document provides an overview of personality type theory, focusing on the Myers-Briggs Type Indicator (MBTI). It discusses Carl Jung's theory of psychological types, which proposed that people naturally have preferences in how they direct their energy (extraversion or introversion), take in information (sensing or intuition), and make decisions (thinking or feeling). The MBTI instrument was created to help identify people's preferences in these four dichotomies based on their self-reported reactions. Together these preferences result in 16 possible personality types that are described. The document also provides statistics on type preferences in the general population.