This chapter describes olefin cross-metathesis (CM) reactions catalyzed by ruthenium, molybdenum, and tungsten complexes and surveys the literature from 1993 through 2020. Cross-metathesis has been applied to the synthesis of a wide range of functionalized alkenes, including natural and biologically active products. Due to its simplicity and inherit atom economy, CM has found applications in the preparation of fine chemicals and various building blocks, and in transformations of biomass. Tandem reactions involving CM as the key step are also reviewed. Examples discussed in this chapter serve to illustrate how the reactivity of alkene substrates in CM depends on the presence of functional groups and steric congestion in the proximity of the reacting double bonds. A discussion of the mechanism of olefin metathesis is also included.