This article provides an overview of exogenous and indigenous inclusions. It discusses the general concepts of phase diagrams, thermochemical relationships, and reaction rates, along with their practical significance. The article describes the most common techniques for controlling the occurrence of inclusions in any cast metal. The article provides a discussion on the inclusions in ferrous and nonferrous alloys. The ferrous and nonferrous alloys include steels, cast irons, aluminum alloys, copper alloys, and magnesium alloys.