| State: | AL |
| Type: | AL |
| Route: | 40 |
| Map Custom: | yes |
| Length Mi: | 21.184 |
| Length Ref: | [1] |
| Established: | 1958 |
| Direction A: | West |
| Direction B: | East |
| Terminus A: | south of Scottsboro |
| Junction: | near Dutton at Henagar |
| Terminus B: | at Hammondville |
| Previous Type: | AL |
| Previous Route: | 39 |
| Next Type: | AL |
| Next Route: | 41 |
State Route 40 (SR 40) is a 21.184adj=midNaNadj=mid state highway in the northeastern part of the U.S. state of Alabama. The western terminus of the highway is at its intersection with SR 35 near Scottsboro. The eastern terminus of the highway is at its intersection with SR 117 at Hammondville, just north of the intersection of SR 117 with Interstate 59 (I-59).
SR 40 travels across the base of Lookout Mountain. The narrow, twisty roadway continues until the highway reaches Dutton in western DeKalb County. East of Dutton, the roadway has fewer curves as it continues across the county. While SR 40 does not directly have an interchange with I-59, there is direct access to I-59 via SR 117 approximately 1miles southeast of the eastern terminus of the highway.