For more than two centuries, the equality between inertial mass and gravitational mass has been a mistery in Physics, until early in the XX century a theory that could explain such equality appeared. In the present work we discuss the concepts concerning those masses, as well as the origin of the theory of General Relativity, which relies in their very equality. The following text is also suitable as a discussion item for high-school and undergraduate students, providing a more solid understanding of the concepts involved.
