Measurement of matrix metalloproteinase (MMP) activity often remains a challenge, mainly in complex media. Two sets of methods are currently used. The first one measures the hydrolysis of natural protein substrates (labeled or not) and includes the popular zymography. These techniques which are quite sensitive, cannot generally be carried out on a continuous basis. The second one takes mainly advantage of the increase of fluorescence, which is associated to the hydrolysis of initially quenched fluorogenic peptide substrates. Quite recently, another group, which is a compromise between the other two, has been developed. It measures the hydrolysis of synthetic triple-helical peptide substrates. These different methods are described and discussed.