| CA Consulting | |
| CAD-Project | Lower Silesian |
| CAD.pl | Silesian |
| CAD/CAM Solution Sp. z o.o. | |
| CafeSuite | Łódź |
| CAIRO-soft Sp. z o.o. | Warmian-Masurian |
| CallPage | |
| Callstack.io Sp. z o.o. | |
| Camel Expert | |
| Cancer Center AI | |
| Candyweb | |
| CANEA Inżynieria i Komputery | Świętokrzyskie |
| Canon Polska Sp. z o.o. | Masovian |
| Capital One Advisers Sp. z o.o. | |
| Capital Service S.A. | |
| Caps | Masovian |
| Captor Therapeutics | |
| Car&More Sp. z o.o. | |
| Cardinal Cryptography Sp. z o.o. | Lesser Poland |
| Cardio 4D | |
| Cardiomatics | |
| Cargill | |
| Cargounit Sp. z o.o. | |
| Carpathia Capital | Greater Poland |
| Carrot Search | |
| Carrywater Group S.A. | Masovian |
| CashDirector S.A. | |
| CashDirector S.A. | |
| Casp System sp. z o.o. | Silesian |
| CBIT Sp. z o.o. | Masovian |
| CC Otwarte Systemy Komputerowe Sp z o.o. | |
| CCA Europe.pl Sp. z o.o. | |
| CD Projectk Red | |
| CD Projekt S.A. | |
| CDN-Partner w Krakowie Sp. z o.o. | |
| cdnet | Lesser Poland |
| CDRmarket | Silesian |
| Celadonsoft | |
| Cellco Communications Sp. z o.o. | West Pomeranian |
| Cellivia 3 S.A. | |
| CelNet | Pomeranian |
| Celon Pharma S.A. | |
| Cemit | Masovian |
| Cenatorium Sp. z o.o. | |
| Cenega S.A. | Masovian |
| CeNTe Sp. z o.o. | Kuyavian-Pomeranian |
| Central and Eastern Europe Data Protection Authorities | Masovian |
| Centrum Astronomiczne im. M. Kopernika Zakład Astrofizyki (CAMK Toruń) Polska Akademia Nauk | |
| Centrum Badań Kosmicznych Polskiej Akademii Nauk | |
| Centrum Badań Molekularnych i Makromolekularnych Polskiej Akademii Nauk | |