Open IoT identity correlation service, or open IoT ICS, is a service to map identities among devices, third party services, and transactions. Recommendation ITU-T Y.4462 specifies the reference architecture of open IoT ICS which supports Internet of things (IoT) devices to access multiple third party service providers. This Recommendation clarifies the concept of the open IoT ICS, identifies its basic capabilities, common requirements and also provides the reference architecture and relevant high-level common procedures for open IoT ICS.