Nepal has conducted several rounds of size estimations in order to estimate the number of key population members with specific risk behaviors. Intrepid Nepal, under the direction of a technical committee under the leadership of NCASC comprising different organizations is conducting the third round of size estimation 2016. The main purpose of this mapping and PSE exercise 2016 is to provide district and national level size estimates of key populations at risk of HIV infection, including Female Sex Workers (FSW), Men who have sex with Men (MSM) and People who Inject Drugs (PWIDs). This mapping exercise will focus on collecting information directly from the hotspots where key populations are found. This study expects to obtain the estimates which will play a crucial role in guiding national level policy makers and planners on effective HIV response in the country.