This Recommendation specifies a flexible interoperable short-reach OTN interface, over which an OTUCn (n ≥ 1) is transferred, using bonded interfaces. The FlexO interfaces are covered by application codes which are at the time of publication 4I1-9D1F, 4L1-9C1F, C4S1-9D1F and 4L1-9D1F in [ITU-T G.695] and [ITU-T G.959.1]. A FlexO group interface complements the existing functions specified in [ITU-T G.709], such as B100G OTUCn frame, ODUk/flex, with new functions such as physical interface bonding, group management and OTUCn (de)mapping. The intent of the FlexO Recommendation is to capture links to existing [ITU-T G.709]/[ITU-T G.798] functions and to provide specifications for new functions that are applicable to FlexO groups. In addition, some introduction material for the addressed application is included.