The early history of the development of the Munsell system is described in this article. This description is based on the information in the notes and sketches in Munsell's color diary, and the Munsell system's development is placed into its historical context. The concept of chroma, new to leading American physicists of Munsell's time, was found to be an original idea of Munsell. All key ideas of the system were developed by Munsell between 1900 and 1904.