| A  | Organization of the work of ITU-T | 
| B  | Means of expression: definitions, symbols, classification | 
| C  | General telecommunication statistics | 
| D  | General tariff principles | 
| E  | Overall network operation, telephone service, service operation and human factors | 
| F  | Non-telephone telecommunication services | 
| G  | Transmission systems and media, digital systems and networks | 
| H  | Audiovisual and multimedia systems | 
| I  | Integrated services digital network | 
| J  | Cable networks and transmission of television, sound programme and other multimedia signals | 
| K  | Protection against interference | 
| L  | Construction, installation and protection of cables and other elements of outside plant | 
| M  | Telecommunication management, including TMN and network maintenance | 
| N  | Maintenance: international sound programme and television transmission circuits | 
| O  | Specifications of measuring equipment | 
| P  | Terminals and subjective and objective assessment methods | 
| Q  | Switching and signalling | 
| R  | Telegraph transmission | 
| S  | Telegraph services terminal equipment | 
| T  | Terminals for telematic services | 
| U  | Telegraph switching | 
| V  | Data communication over the telephone network | 
| X  | Data networks, open system communications and security | 
| Y  | Global information infrastructure, Internet protocol aspects and next-generation networks | 
| Z  | Languages and general software aspects for telecommunication systems |