Advances in gallium nitride (GaN) device technology over the last 25 years have enabled commercial radio frequency (RF) applications to benefit from its high-power handling capability and speed. Because of these advances, GaN has emerged as a leading technology for future 4G and 5G communications systems. This presentation will cover GaN device technology starting with the basics of GaN materials and device structures. It will show how the step-function improvement in materials and device capability with GaN translates to step-function advances in system capability. It will then give examples of GaN power amplifier applications for present day 4G wireless communications applications. Along the way, the presentation will address industry progress that has enabled GaN technology to become commercially viable. Finally, the presentation will preview opportunities for GaN technology in future 5G communications applications.