Acoustic wave devices coated with a biolayer represent one biosensor approach for the detection of medically relevant biomolecules. In a typical application, the acoustic wave device is connected in an oscillator circuit, and the frequency shift Δf resulting from a biomolecular event is recorded. We discuss our recent work in this field, which has included the use of Rayleigh wave surface acoustic wave devices for vapor phase detection as well as quartz crystal microbalance devices for liquid phase measurements. For all of the results reported herein the biofilm on the surface of the acoustic wave device consists of a layer of antibodies raised against a specific target molecule or antigen. We present our results for the vapor phase detection of small molecules such as uranine and cocaine as well as liquid phase detection of small and large molecules. The data we present from these various experiments is the signature associated with the biomolecular recognition events; that is, we record and present Δf(t). Finally, we present the recent results of our time-dependent perturbation theory work, which gives a potential method for resolving the acoustic wave biosensor signature into information relating to molecular structure changes during a molecular recognition event.