India's Unified Payments Interface, better known as UPI, is an instant digital-payment system developed by the National Payments Corporation of India. It allows people to move money directly between bank accounts through participating apps.
The key idea is interoperability. A user can have an account at one bank, use an app from another company and still send money to a person or merchant whose account is held elsewhere in the banking system.
Instead of repeatedly entering long bank-account numbers, users can often pay with a virtual payment address, phone-linked identity or QR code. The system routes the instruction between participating banks and settles the transaction through the UPI network.
UPI is not itself a bank account and it does not hold all users' money in one central wallet. The money normally moves between underlying bank accounts. Apps provide the customer interface, while banks and the payment infrastructure handle authorisation and settlement.
Security depends on several layers, including device access, bank authentication and transaction approval. Users still need to protect their credentials and avoid approving fraudulent payment requests.
UPI's success comes from making many banks and apps work on a common system. That creates convenience but also raises questions about fees, competition, market concentration, fraud prevention and access for small merchants.
A common misconception is that every payment app owns the UPI network. In reality, the underlying system is operated by NPCI, while banks and payment apps connect to it.
The easiest way to understand UPI is as a shared payment railway: different banks and apps can use the same tracks to move money quickly between accounts.