This document provides an introduction to mobile virtual network operators (MVNOs). It defines an MVNO as a company that buys network capacity from a mobile network operator to offer its own branded mobile subscriptions and services, but does not own its own spectrum. The document outlines the concept of MVNOs, their formation, types including full, enhanced and basic MVNOs. It also discusses the generic MVNO model and opportunities and risks for MVNOs, providing examples of ESPN Mobile and Virgin Mobile India.