Impedance may refer to:
- Electrical impedance, the ratio of the voltage phasor to the electric current phasor, a measure of the opposition to time-varying electric current in an electric circuit
- Characteristic impedance of a transmission line
- Nominal impedance, approximate designed impedance
- Wave impedance, a constant related to electromagnetic wave propagation in a medium
- Impedance of free space, a universal constant
- Mechanical impedance, a measure of opposition to motion of a structure subjected to a force
- Acoustic impedance, a constant related to the propagation of sound waves in an acoustic medium