| Český telekomunikační úřad | |
| Český Webhosting s.r.o. | Central Bohemian |
| CESNET, z. s. p. o. | |
| CeSYS | |
| CEVRO Institut, z.ú. | |
| ČEZ, a.s. | Plzeň |
| Chaos Czech, a.s. | |
| Chaps, s.r.o. | South Moravian |
| Charles University - Faculty of Mathematics and Physics | Prague |
| Charles University - School of Computer Sciences | Prague |
| Charlie Monroe Software, s.r.o. | |
| Chip.cz | Prague |
| Choice QR | |
| CircleTech, s.r.o. | Prague |
| CIT.CZ, spol. s r.o. | Prague |
| CityTel, s.r.o. | Prague |
| Clever Soft, s.r.o. | Prague |
| CleverMaps | |
| CleverTech, s.r.o. | |
| client.IO | Prague |
| Cloud4com, s.r.o. | |
| CloudSailor, s.r.o. | |
| Clyde | Prague |
| CMS Consulting s.r.o. | Central Bohemian |
| CNC Praha, s.r.o. | Prague |
| CNW Network, s.r.o. | Prague |
| CocoMedia | Prague |
| Codasip | |
| Code Secure, s.r.o. | Prague |
| Codeblox, s.r.o. | |
| Codeon Soft, spol. s r.o. | |
| Coderz.cz | |
| Codeware, s.r.o. | Prague |
| Coding Bootcamp Praha | Prague |
| Codium One, s.r.o. | |
| COex | |
| cognito.cz, s.r.o. | South Moravian |
| COGRAS, spol. s.r.o. | |
| Colsys, s.r.o. | |
| Com-Sys TRADE, spol. s r.o. | |
| Comfor Stores, a.s. | South Moravian |
| Comfort Space, a.s. | |
| Comin.cz, s.r.o. | Prague |
| Comlinks, s.r.o. | Prague |
| Commity.cz, s.r.o. | |
| Compas automatizace, spol. s r.o. | Vysočina |
| COMPEKON, s.r.o. | Olomouc |
| Complet, a.s. | Prague |
| Comprimato Systems, s.r.o. | |
| Compunax, spol. s r.o. | |