| # | Company name | Role | # of projects |
|---|---|---|---|
| 421 | C. J. Jeppesen | Consultancy | 1 |
| 422 | C.A. Peerman | Consultancy | 1 |
| 423 | C.c Winningham Corp. | Consultancy | 1 |
| 424 | Cad Reprographics | Consultancy | 1 |
| 425 | Cain T Square (cts) Reprographics | Consultancy | 0 |
| 426 | Calcinotto & Associates Ltd. | Consultancy | 0 |
| 427 | Calenberg Ingenieure GmbH | Consultancy | 0 |
| 428 | California Geo/systems Inc | Consultancy | 1 |
| 429 | Calleva Design | Consultancy | 0 |
| 430 | Calvin E Cowher M.s.e P.e | Consultancy | 1 |
| 431 | Camali Corporation | Consultancy | 1 |
| 432 | Cambridge Architectural Research Limited | Consultancy | 0 |
| 433 | Camelot Business Document Services | Consultancy | 1 |
| 434 | Cameron Taylor | Consultancy | 9 |
| 435 | Cameron Taylor Bedford | Consultancy | 0 |
| 436 | Cameron Taylor Bedford | Consultancy | 0 |
| 437 | Cameron Taylor Bedford | Consultancy | 0 |
| 438 | Cameron Taylor Bedford | Consultancy | 0 |
| 439 | Cameron Taylor Bedford | Consultancy | 0 |
| 440 | Cameron Taylor Bedford Limited | Consultancy | 0 |