Due to its simplicity, this lecture note is intended to be a source of introductory reference for students of the faculty of administrative, accounting and related sciences on one of the elements that make up the markets: the demand. It shows the definitions and types of demand, the law of demand, graphic and mathematical analysis. This is done through simple examples that link the theoretical-practical and its impact on markets. The theory of demand serves as a fundamental pillar in the field of Economics, aiming to comprehend and predict consumer behavior patterns. This document introduces into the intricacies of demand theory, shedding light on its key components and the factors that influence consumer preferences and choices.