A unified response theory for the time-resolved nonlinear light generation and two-photonphotoemission (2PPE) from metal surfaces is presented. The theory allows one to describethe dependence of the nonlinear optical response and the photoelectron yield, respectively,on the time dependence of the exciting light field. Quantum-mechanical interference effectsaffect the results significantly. Contributions to 2PPE due to the optical nonlinearity of thesurface region are derived and shown to be relevant close to a plasmon resonance. Theinterplay between pulse shape, relaxation times of excited electrons, and band structure isanalysed directly in the time domain. While our theory works for arbitrary pulse shapes,we mainly focus on the case of two pulses of the same mean frequency. Difficultiesin extracting relaxation rates from pump–probe experiments are discussed—forexample due to the effect of detuning of intermediate states on the interference. Thetheory also allows one to determine the range of validity of the optical Blochequations and of semiclassical rate equations, respectively. Finally, we discuss howcollective plasma excitations affect the nonlinear optical response and 2PPE.