The Internet Group Management Protocol (IGMP) is a communication protocol used by hosts and adjacent routers on an Internet Protocol (IP) network. Its primary function is to manage the membership of hosts in Internet Protocol multicast groups, allowing efficient data transmission to multiple recipients simultaneously. IGMP operates at the Network Layer of the Internet Protocol Suite and helps routers determine which hosts are interested in receiving multicast traffic. By sending IGMP messages, devices can join or leave multicast groups, ensuring that data is only sent to those who want to receive it, thus optimizing network resources.