The formation of microbial biofilms on the surface of teeth involves a complex set of processes beginning with the initial adhesion of cells to the acquired enamel pellicle, a conditioning layer of proteins and glycoproteins that remains permanently bound to the tooth surface. Interspecies associations are critical for the subsequent growth and proliferation of microbial cells to form biofilms on the tooth surface. Physical cell-cell binding between taxonomically distinct microorganisms (‘coaggregation’) is thought to drive the spatial positioning of cells in the biofilm. In addition, cell-cell interactions are sensed by the participating microbes leading to contact-dependent gene regulation. This is layered on top of a wide variety of other sensing systems that enable microorganisms to sense and respond to the physical and chemical environment within oral biofilms. This chapter discusses the key molecular, cellular and ecological factors that modulate the formation of biofilms on tooth surfaces and considers the opportunities for interventions that prevent the transition from oral health to disease.