The Unified Payments Interface (UPI), is a real-time Indian payment system that enables immediate fund transfers between bank accounts using a mobile device. Since its introduction in 2016, UPI has transformed the digital payment ecosystem in India, offering a unified platform for seamless, real-time transactions across multiple banks and payment service providers enabling India's goal of becoming a less cash economy. The system has gained immense popularity in India over the last eight years, and has helped to promote financial inclusion and economic development in the country. With over 300 million UPI users in India, the system has positioned the country to the forefront of real-time payment transactions globally. Projections by PwC, a leading consultancy firm, suggest that daily UPI transactions in India are set to reach one billion by the financial year 2026–27, accounting for approximately 90 per cent of all non-cash transactions. In this chapter, the evolution of the Indian UPI system is examined alongside its uniqueness, the rationale behind its success, and a comparison with some of the leading mobile-based payment services across Asian countries.