| Blanchefosse-et-Bay | |
| Commune Status: | Commune |
| Image Coat Of Arms: | Blason Blanchefosse-et-Bay.svg |
| Arrondissement: | Charleville-Mézières |
| Canton: | Signy-l'Abbaye |
| Insee: | 08069 |
| Postal Code: | 08290 |
| Mayor: | Romuald Petit[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | Ardennes Thiérache |
| Coordinates: | 49.7781°N 4.2367°W |
| Elevation M: | 255 |
| Elevation Min M: | 170 |
| Elevation Max M: | 278 |
| Area Km2: | 20.47 |
Blanchefosse-et-Bay (in French pronounced as /blɑ̃ʃfos e bɛ/) is a commune in the Ardennes department and Grand Est region of north-eastern France.