Time-dependent density-functional theory (TDDFT) is an extension of density functional theory (DFT) to time-dependent problems, and can be viewed as an alternative formulation of time-dependent quantum mechanics. The use of TDDFT is increasing, and it is fast becoming one of the tools of choice to get accurate and reliable predictions for excited-state properties in solid state physics, chemistry and biophysics, both in the linear and non-linear regimes. This interest has been motivated by the recent developments of TDDFT (and time-dependent current functional theory) and include the description of photo-absorption cross section of molecules and nanostructures, electron-ion dynamics in the excited state triggered by either a small or high intense laser fields, van der Waals interactions, development of new functionals coping with memory and non-locality effects, applications to biological systems, transport phenomena, optical spectra of solids and low-dimensional structures (as nanotubes, polymers, and surfaces), etc.