Unified Payments Interface (UPI) is a payment system launched by National Payments Corporation of India
and regulated by Reserve Bank of India which facilitates the fund transfer between two bank accounts on the mobile platform instantly.
UPI (Unified Payments Interface) is an advanced version of Immediate Payment Service(IMPS) platform designed for transferring funds using:
Transfer through Virtual Payment Address (Unique ID provided by bank)
or Account Number + IFSC or Mobile Number + MMID(Mobile Money Identifier)
or Aadhaar Number or Collect / Pull money basis Virtual ID.
A MPIN(Mobile banking Personal Identification number) is given to the banking customer once they register for UPI which is required to be entered while confirming a money transfer.
Banks supporting UPI payment have started to upload their own UPI enabled Apps on Google Play store as well as on Apple App Store also.
National Payments Corporation of India has launched a Payment app BHIM and NUUP service for performing transaction using Aadhaar number over UPI.
Banks which supports UPI based transaction have been listed in NPCI page : http://www.npci.org.in/UPI_Livemembers.aspx