Silylenes 2 or 4, generated by thermolysis of cyclotrisilanes 1 and 3, were inserted into the SiCl or SiH bonds of monosilanes to yield a variety of disilanes, which can be further functionalized subsequently. In a few cases, trisilanes are accessible by the reaction of 1 with disilanes. The reaction of a metalated silane with a chlorosilane is an alternative method for the formation of SiSi bonds