In feedback controls, the controlled output of a device is measured and fed back for use in a control computation. We utilize feedback controls in a variety of applications ranging from LLRF to synchronization of optical pulses with femtosecond accuracy over kilometers of fiber, and beam-based feedback applied to Linac-driven Free Electron Lasers (FELs). We have particular expertise in the use of feedback controls for particle accelerators, which is essential to modulate various physical quantities in the presence of external disturbances such as variations in temperature, pressure, variability of electronic components, mechanical couplings, etc. The orbit of particles in an accelerator and other parameters influencing performance of the beam are also controlled using feedback.