Laser absorption is reviewed in the context of fast ignition inertial fusion. This leads us to consider laser absorption by overdense plasmas for values of intensity times wavelength squared (Iλ2) greater than 1010 W (1018 W cm−2 µm2), which corresponds to the onset of relativistic electron motion in the laser fields. A collection of published absorption values obtained in laser–solid experiments and in numerical modelling of laser–plasma interactions is presented.