In the following paper I present an analysis of the origins of zoning laws and a case study of the beginning of zoning in Berkeley, California. The particular focus of the article is on the role of large-scale land subdividers, or "community builders", and on their economic and political activities both as entrepreneurs and as members of local real estate boards. The case of Berkeley demonstrates the key actions of one prominent community builder, Duncan McDuffie, as a promoter of local planning and zoning to facilitate the development and marketing of high-income residential subdivisions. The case illustrates both the contribution of zoning as an innovation in land planning and regulation, as well as some of its social implications as practiced in the 1910s and 1920s.