| A | Organization of the work of ITU-T | 
| D | Tariff and accounting principles and international telecommunication/ICT economic and policy issues | 
| 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 | Environment and ICTs, climate change, e-waste, energy efficiency; 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 | Telephone transmission quality, telephone installations, local line networks | 
| Q | Switching and signalling, and associated measurements and tests | 
| 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, next-generation networks, Internet of Things and smart cities | 
| Z | Languages and general software aspects for telecommunication systems |