This document describes internal and external interfaces of CubeSat. The internal interface includes the interface between components and the interface between a CubeSat platform and a mission payload. The external interface is limited to the umbilical connectors, i.e. access port. The document also describes the items to be included in the datasheet of the CubeSat components and platforms. The datasheet requirements apply to catalogued commercial products ready for sale. This document does not cover the interface between CubeSat and its deployer, i.e. POD. This document is applicable to CubeSats of all sizes.