Systems and methods of downhole power generation are disclosed, which provide for the generation of electrical power in a downhole environment by the use of an electrical generator coupled to a hydraulic circuit that receives energy from a source in the downhole environment. The hydraulic circuit can receive energy from flowing drilling fluid and/or from kinetic energy of one or more portions of the drill string. A direct or indirect coupling can be used to transfer energy from the downhole environment to a pump in the hydraulic circuit, which can act as a hydraulic flow source, providing flow through a flow regulation device or control circuit. The hydraulic fluid under such control can then be used to turn a hydraulic motor, which is used to turn an electric generator for the generation of electricity for downhole tools such as logging tools, related telemetry, and the like.