The chapter reviews the studies on source apportionment conducted in the Indian sub-continent focussing mainly on respirable particulate matter including their sources and characteristics. The receptor models used in identification of major sources of respirable particulate matter and their fractions are also comprehensively described. Among the countries in the Indian sub-continent, India has carried out the greatest number of studies, including spatio-temporal variations, characterization and apportionment of the particulate matter sources. However, in Pakistan, the primary focus has been given towards apportionment of particulate matter, which has mainly been carried out in two mega cities, i.e. Lahore and Karachi. In Sri Lanka, Bhutan, Nepal and the Maldives, a limited number of studies have been carried out specifically targeting the apportionment of particulate matter. However, the existence of climate observatories in Nepal and Maldives is an added advantage towards possibilities of planning and conducting comprehensive studies investigating the particulate matter characteristics and their sources.