In this chapter, we explore how light from sources such as the sun or a lamp can be dispersed into its spectral components. We discuss various dispersive elements, including gratings and prisms, and the phenomena of refraction and diffraction that allow these elements to spatially separate light. The chapter explores blackbody radiation and the historical significance of the ultraviolet catastrophe. Additionally, we introduce the concepts of absorption and emission lines, which provide insights into atomic and molecular energy levels.