This specifiation is applicable to fibre optic brancing devices. These have all of the following general features:- they are passive in that they contain no optoelectronic or other transducing elements;- they have three or more ports for the ingress and/or egress of optical power and share optical power among these ports in a predetermined fashion;- the ports are optical fibres or optical fibre connectors.In this generic specification, fibre optic branching devices are classified by wavelength dependance into two sub-families; wavelength selective devices and non-wavelength selective devices, each of which will be covered by a seperate blank detail specification.