Microbial biofilms are governed by an intricate interplay between physical-chemical factors and the physiological and genetic properties of the inhabiting microbes. Many of the physiological traits that are exhibited in a biofilm environment have been observed and studied previously in detail in planktonic cultures. However, their differential and combinatorial phenotypic expression in distinct subpopulations localized to different regions in a biofilm is the cause for the overall biofilm heterogeneity. In this chapter, the causes and consequences of this interplay are elaborated with a special focus on processes controlling biofilm stability and dispersal.