Ambient mass spectrometry (ambient MS) is a powerful and rapidly growing new field that provides high sensitivity MS directly from surfaces at ambient pressure. There is now a rich evidence base in the published literature of the success of these methods for forensic analysis including: detection of explosives at nanogram levels; chemical composition of counterfeit pharmaceutical tablets, detection of drugs of abuse from biological liquids such as urine and plasma; breath analysis of metabolites; and imaging analysis for document verification and fingerprint identification. Recent developments in miniaturised (shoe-box sized) mass spectrometers have enabled these developments to be translated to portable on-scene detection and first responder usage. In this review, we illustrate and compare the effectiveness of the most popular and promising techniques of desorption electrospray ionisation (DESI), direct analysis in real time (DART), plasma assisted desorption ionisation (PADI) and extractive electrospray ionisation (EESI). Forensic analysis by its very definition must stand up to scrutiny in a court of law. It is therefore essential that measurements are repeatable, valid, traceable and fit for purpose. The establishment of a measurement infrastructure is therefore essential to ensure that the methods used may be accredited and conform to relevant quality systems and procedures. © Crown copyright 2009. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.