Microorganisms are living colloids, which colonize diverse environments; for example, bacteria form biofilms at fluid interfaces. Biofilms are complex and well-organized multicellular structures, which confer to cells residing at interfaces environmental advantages promoting cell survival. Drawing on our understanding of classical colloids at interfaces, we seek to understand the dynamics and complex rheology that bacteria introduce to both classic and unconventional interfaces, and to identify and exploit potentials of interaction not afforded by classical colloids. We are exploring the interactions of both biofilm-creating and planktonic bacteria with oil-water and aqueous-aqueous interfaces. These studies incorporate physical and biological approaches to describe interfacial film formation and develop strategies that would control or alter film properties, or that impede bacterial infections, or promote hydrocarbon degradation, relevant to novel self-healing materials, medical and environmental applications.