This part of IEC 61758 provides general information and guidance on the subject of closures. It includes references, general closure and interface descriptions and definitions. This standard defines the following general interfaces for closures: - interface to cables; - interface to FMS; - interface to parts other than FMS or cables; - interface to external sitings (pits, manholes etc.) This specification covers all types of closures. The performance requirements are given in IEC 61753-111 series (in preparation). This closure standard allows both single mode and multi-mode fibre to be used, and covers all IEC standard optical fibre cables as listed in Clause 2, with their various fibre capacities, types and designs. Figure 1 shows and defines the interface between the closure and the fibre management system.