Two types of silylcarbocyclization reactions (SiCaCs) of 1,6-diynes are discussed : (i) silylcarbocyclization-hydrosilylation (SiCaC-HS) reactions giving 3-(silylmethylene)-4-(silylmethyl)pyrrolidine, 3-(silylmethylene)-4-(silylmethyl)tetrahydrofuran, 3,4-bis(silylmethyl)-3-pyrroline, and 1,2-bis(silylmethyl)-4,4-dicarbethoxycyclopentene; and (ii) silylcarbobicyclization (SiCaB) reactions yielding a variety of carbocyclic and heterocyclic bicyclo[3.3.0] systems. Mechanisms for these SiCaC-HS and SiCaB processes are proposed.