The enormous amounts of infrared (IR) radiation emitted by luminous infrared galaxies (LIRGs, L_IR=10^11-10^12Lsun) and ultraluminous infrared galaxies (ULIRGs, L_IR>10^12Lsun) are produced by dust heated by intense star formation (SF) activity and/or an active galactic nucleus (AGN). The elevated star formation rates and high AGN incidence in (U)LIRGs make them ideal candidates to study the interplay between SF and AGN activity in the local universe. In this paper I review recent results on the physical extent of the SF activity, the AGN detection rate (including buried AGN), the AGN bolometric contribution to the luminosity of the systems, as well as the evolution of local LIRGs and ULIRGs. The main emphasis of this review is on recent results from IR observations.