Hydrosilylation of alkenes represents a commercially important method for preparing organosilicon compounds. The process is mechanistically similar to the hydrogenation of alkenes. In fact, similar catalysts are sometimes employed for the two catalytic processes.
The prevalent mechanism, called the Chalk-Harrod mechanism, assumes an intermediate metal complex that contains a hydride, a silyl ligand (RSi), and the alkene substrate.  Oxidative addition proceeds by the intermediacy of a sigma-complex, wherein the Si-H bond is not fully broken.
Hydrosilylation of alkenes usually proceeds via anti-Markovnikov addition, i.e., silicon is placed at the terminal carbon when hydrosilylating a terminal alkene  Variations of the Chalk-Harrod mechanism exist.  Some cases involve insertion of alkene into M-Si bond followed by reductive elimination, the opposite of the sequence in the Chalk-Harrod mechanism.  In certain cases, hydrosilylation results in vinyl or allylic silanes resulting from beta-hydride elimination.
Alkynes also undergo hydrosilylation, e.g., the addition of triethylsilane to diphenylacetylene:
:EtSiH  +  PhC≡CPh   →  EtSi(Ph)C=CH(Ph)