Robust Control Theory is a branch of control theory that focuses on designing systems that can maintain performance despite uncertainties and variations in their environment. It aims to ensure that a control system remains stable and effective even when faced with unexpected changes, such as disturbances or model inaccuracies. This theory is particularly useful in engineering applications, where systems must operate reliably under varying conditions. By using techniques like H-infinity methods and mu-synthesis, engineers can create controllers that are less sensitive to uncertainties, ensuring that the system behaves predictably and meets performance specifications.