This tutorial review deals with the design of molecular receptors capable of molecular recognition at the gas-solid interface, to be used as selective layers in gas sensors. The key issue of specific versus nonspecific binding in the solid layer is discussed in terms of cavity inclusion and layer morphology. The combined use of mass spectrometry and crystal structure analysis provide accurate information on type, number, geometry and strength of receptor-analyte interactions in the gas phase and in the solid state. From these data, the gas sensing properties of a given receptor toward a single class of analytes can be anticipated.