The RF transmit chain is one of several “black box” systems in the MRI scanner. The implementation of the RF transmit chain has remained fairly consistent since the earliest clinical MRI scanners. The advent of parallel transmission (pTX) provides a compelling opportunity to rethink not only the design of the RF power amplifiers (RFPAs) and coils, but of the entire MRI scanner. In this lecture we will review fundamental RFPA concepts such as linearity and efficiency. We will then explore advanced topics relating to pTX, including control, decoupling, local amplifiers, and switchmode amplifiers.