Oral biofilms consist of microbial cells enmeshed in a three-dimensional extracellular matrix. The matrix provides a scaffold for microbial cell adhesion while modulating the growth, survival, and metabolic activity of the biofilm community. This chapter highlights current knowledge about the composition of extracellular matrix and its role in the development, physicochemical properties, and functional traits of oral biofilms, which can modulate the microbial community virulence associated with oral diseases.