Mahasu Pahari is a Western Pahari language spoken in Himachal Pradesh. It is also known as Mahasui or Mahasuvi. The speaking population is about 1,000,000 (2001). It is more commonly spoken in Himachal Pradesh's Shimla and Solan districts, in western parts of Uttarkashi district in Uttarakhand and in Kalka and Pinjore of Panchkula district in Haryana. It is to be known that Shimla and Solan were parts of the old Mahasu district. Himachal Pradesh State on 1 September 1972 reorganised the districts dissolving Mahasu district. The Solan district was carved out of Solan and Arki tehsils of the then Mahasu district and tehsils of Kandaghat and Nalagarh of the then Shimla District of Punjab.