The investigation of the development and the properties of biofilms is difficult because classical microbiol. does not offer non-destructive methods other than microscopical observations. This paper discusses the use of different Fourier transform IR spectroscopy (FTIR-spectroscopy) techniques as a means to investigate microorganisms in biofilms. FTIR-spectroscopy is suitable for the identification of microorganisms and presents a new addn. to taxonomic and genetic methods. The FTIR anal. of bacterial isolates provides fingerprint spectra, allowing the rapid characterization of microbial strains. Secondly, the FTIR-attenuated total reflection (ATR) technique can be used for the observation of biofilms forming directly on the interface of an ATR crystals such as germanium. These crystals can be coated to obtain a surface more relevant to study interfacial processes. Spectra can be acquired non-destructively, in situ and in real time. This method is suitable for fundamental biofilm research, as well as for monitoring of biofilm formation, e.g., in an ultrapure or drinking water systems. Furthermore, FTIR-ATR also allows the rapid anal. of deposits on surfaces, e.g., filtration membranes. The anal. discrimination between microorganisms, inorg. material or other foulants can be obtained. Thirdly, with the diffuse reflectance technique (DRIFT) it is possible to investigate reflecting surfaces like metals or very small samples. The compn. of surface coatings like biomass or other surface contaminants can be detected. These different measurement techniques demonstrate that FTIR -spectroscopy is suitable for biofilm and surface anal. and can be applied in many different ways.