In this talk, I will first review the matrix element method, which has been intensively used at the Tevatron during the past few years, either to disentangle signal from background events or to measure accurately particle properties in decay-chain processes. In this method, one discriminates between different theoretical assumptions by defining a weight for each experimental event, based on the squared matrix element. As this technique makes use of the whole information reconstructed from the detector, it is particularly suitable for the analysis of low statistics events and/or experimental signatures characterized by a large amount of missing transverse energy.