In the other direction, driving a 3.3V input from a 5V output you might expect that a level shifting circuit would be required, and in many cases you would be right. But before reaching for that ...

Figure 5: OUT to IN operation in proposed bi-directional level shifter. Voltage range : 0.9v to 1.32v & 1.32v to 0.90v Models – best, worst, typ, bpwn,wnwp. Timing parameters are measured at wcs, 150C ...