There has been an increasing trend in recent years towards miniaturisation in mass spectrometry. Miniature versions of time of flight (TOF), magnetic sector and quadrupole ion trap have all been demonstrated. The use of silicon integrated circuit fabrication techniques (MEMS) has led to microengineered (submillimetre) versions of many of the more popular mass spectrometers including crossed field, travelling wave and quadrupole (QMS) instruments. In this presentation a brief survey of the various miniature systems which have been or are being developed will be given and their potential for use in residual gas analysis will be assessed. Recent results arising from the UK microengineered QMS project will also be presented and discussed. The performance and reliability of microengineered single-element quadrupole devices have both been raised considerably by improved construction methods. The mass range was raised from 50 to 150 amu, and the mass resolution was increased to 70 (measured at 10% peak height). Sensitivity was enhanced by an order of magnitude using a miniature multiplying detector. The useable pressure range has been established and modelled. Ion coupling was optimised by using software simulations (SIMION), and several different miniature ion sources have been investigated. Array-type devices containing either nine parallel quadrupoles or five independent mass filters have been developed, together with a self-aligning ion detector array. Theoretical simulations of the microengineered QMS have been undertaken by computing the trajectories of large numbers (>10,000) of ions injected into the mass filter and show that the experimental performance for a range of operating conditions may be successfully modelled.