Concepts for breaking a complex system into discrete components have been widely researched and many methods of interoperability have been developed for realising modularity approaches where different parts can be easily connected, configured, and re-configured to achieve different functionalities. The methods are wide ranging but due to their individualist nature do not have wide appeal and rarely get adopted. Similarly, organizations develop supply chains where the parts needed have their own customised interfaces so that they can be sourced from specialised manufacturers. These supply chains tend to be specific to individual manufacturers and components cannot be easily used by other organisations. The chapter presents modularity guidelines being developed by ISO TC299/WG6 for service robots. The guidelines consider hardware, software, and composite aspects of how connectivity and functionality requirements should be achieved. Safety and security aspects are also included in the guidelines.