This chapter gives an overview of sampling ambient air using passive (also termed diffusive) samplers. The use of this type of sampler in ambient air monitoring has become very popular due to the simplicity and convenience in terms of its deployment. Although the use of these samplers requires the back up of a good analytical laboratory for preparation and analysis, the site operational requirements are very basic. The popularity of passive sampling is strongly linked to the fact that it can be easily deployed at remote and/or high risk environments and is less susceptible to damage or theft. These samplers have added advantages in that they are small in size, light in weight, silent in operation, cost effective and do not require any electricity or field calibration. They can also easily be deployed by non-specialists which make the spatial and temporal collection of data over long time periods possible. The basic principles, sampler network design, methodology, quality assurance and a few case studies are discussed.