Spectroscopy is at the root of modern planetology, in that it gives access remotely to the possibility to analyze the physical properties of planets. Today, the spectacular advance in techniques and models available to planetology reach an accuracy giving access to new domains in planetary physics, as meteorology, physico-chemical processes, etc. This article is centred on the infrared spectroscopy techniques. It will describe some of the physical observables accessible to modern instrumentation, in space or from the ground. The theoretical as well as instrumental limitations will be given, and the expected progress in short or medium term will be described. To cite this article: P. Drossart, C. R. Physique 6 (2005).