This paper presents the development of Grid Code requirements for new and renewable forms of generation in Great Britain (GB). After briefly describing the background to the GB Transmission System and the volume of renewable generation which is anticipated to connect in the future, the paper discusses the Grid Code and Grid Code change process. In particular, the paper discusses the interfaces with key stakeholders, the technical issues considered in connecting other generation technologies to the Transmission network and the rationale for the final Grid Code requirements. The technical issues discussed include fault ride through, frequency range, frequency response, power/frequency characteristic, reactive range, voltage control and power quality. The paper concludes with the experiences gained in the connection of wind generation projects to the GB Transmission System both before and after the approval of new proposals to the GB Grid Code.