In situ particle monitors (ISPMs) have been developed and evaluated by installing thern onto a variety of vacuum tools. It has been shown that the ISPM's enable: (1) detection of sporadic particles in vacuum chambers, (2) specification of particle sources, (3) detection of tool maintenance cycles, and (4) optimization of chamber venting conditions. In the process of evaluating the ISPM's, it has become clear that particle counts measured by ISPM sensors significantly depend on the location where the sensors are installed. As a result of a comparison between the ISPM particle counts and particle-per-wafer-pass particle counts, it has been found that there is a correlation between the two measurements. However, ISPMs offer a broad range of advantages in respect of the reduction of the cost of ownership and being provided real time measurement, and therefore, it is implied that ISPMs have the potential to replace or supplement monitor wafer measurements.