The protocol that governs how data is transmitted over the internet is the Transmission Control Protocol/Internet Protocol (TCP/IP). TCP/IP is a suite of communication protocols that enable computers and devices to communicate across networks, ensuring reliable data transmission. It breaks down data into packets, which are then sent over the network and reassembled at the destination. This protocol is foundational to the internet and supports various applications such as web browsing, email, and file transfer. Its robust error-checking and data integrity features make TCP/IP essential for reliable internet communications.