Electron cyclotron heating (ECH) has proved to be a very flexible system for heating applications in DIII-D. The outstanding characteristics of ECH - controllable heating location, a high degree of localization of the power, ability to heat without introducing particles, and ability to heat only the electron fluid - have been used in a wide variety of experiments to study wave physics and transport, to control magnetohydrodynamic activity, and to improve discharges. These characteristics along with relatively easy coupling to the plasma make ECH a valuable resource for both heating and instability control in burning plasmas.