Laser Desorption Postionization for Imaging Mass Spectrometry is used to probe bacterial biofilms and other complex molecular surfaces. We combine 7.87 eV vacuum ultraviolet postionization and chemical derivatization for the selective ionization of small molecule analytes in complex mixtures. C60 ion beams are also used to depth profile these materials. Laser desorption postionization is compared with established methods of imaging mass spectrometry such as matrix-assisted laser desorption ionization and cluster secondary ion mass spectrometry. We are using these and related strategies for the analysis of quorum sensing species and antibiotics in bacterial biofilms to probe antibiotic resistance mechanisms in biofilms. We are also examining the role of bacterial biofilms in the degradation of dental composites within the oral cavity.