This document provides an overview of regenerative braking systems. It begins with an introduction and history section describing early patents and developments. The principles and components of regenerative braking are then explained, noting that kinetic energy is converted to electrical energy during braking via electric motors or hydraulic pumps. Applications in electric vehicles, hybrids, and locomotives are discussed. The benefits include improved efficiency and emissions reductions, while costs and complexity are disadvantages. Regenerative braking effectively improves vehicle performance by recapturing kinetic energy.