Motion Control Synchronization SERCOS III specifies a profile for distributed control functions in modular machines and systems, providing for controller-to-controller synchronization between distributed motion controls. This addresses the increased need in manufacturing systems engineering in which individual machine modules not only need to be connected mechanically, but also need to be integrated into communication networks and coupled in hard real-time. Manufacturer-specific solutions -- based on available SERCOS interface physics -- existed for synchronization between distributed motion controls. With the SERCOS C2C (Controller-to-Controller Synchronization and Communication) Profile, this type of communication is now standardized. The C2C Profile is a supplement to the existing SERCOS device profiles for servo drives and remote I/O devices. The specification of communication and synchronization mechanisms between distributed motion controls takes into consideration the hardware redundancy and hot-plugging features of SERCOS III. In addition, the data and commands exchanged between controls are defined based on the existing SERCOS parameter model. This data includes control and state information, as well as relevant command values and actual values. In this context, a convergence with the CIP Motion Profile and the development of a SERCOS/CIP-Gateway is planned. Typical applications for such a profile are in printing, packaging and processing machines; as well as machine tools with special requirements for control systems and synchronization, e.g., machine concepts with gantry axes or rotary transfer tables.