After a review of the many effects of metallicity on the evolution of rotating and non-rotating stars, we discuss the consequences of a high metallicity for massive-star populations and stellar nucleosynthesis. The most striking effect of high metallicity is to enhance the amount of mass lost by stellar winds. Typically, at a metallicity of Z = 0.001 only 9% of the total mass returned by non-rotating massive stars is ejected by winds (91% by supernova explosions), whereas at Solar metallicity this fraction may amount to more than 40%. High metallicity favors the formation of Wolf–Rayet stars and Type-Ib supernovae, but militates against the occurrence of Type-Ic supernovae. We estimate empirical yields of carbon on the basis of the observed population of WC stars in the Solar neighborhood, and obtain that WC stars eject 0.2%–0.4% of the mass initially locked into stars in the form of newly synthesized carbon. Models give values well in agreement with these empirical yields. Chemical-evolution models indicate that such carbon yields may have an important impact on the abundance of carbon at high metallicity.