The potential energy surfaces for the insertion reactions of silylene into NH3, Hp, HF, PH3, H2S, and HCl have been characterized in detail by using ab initio molecular orbital theory, including electron correlation and zero-point corrections. All the interactions involve the initial formation of a donor-acceptor complex followed by a proton shift via an unsymmetrical high-energy transition state. The binding energies of the complexes as well as the rearrangement barriers for the hydrogen migration of these complexes to give the normal valent compounds have been calculated in all cases. The complex between SiH2 and NH3 exists in a deep minimum with a high barrier for rearrangement (38 kcaljmol) and is predicted to be a suitable candidate for spectroscopic observation. The silylene complex with PH3 also involves a fairly deep minimum, but the overall insertion barrier is small. The interaction between SiH2 and H20, widely studied experimentally, involves a complex with a fairly high rearrangement barrier (22 kcaljmol). The interactions with H2S, HF, and HCl are fairly weak with lower calculated rearrangement barriers (13, 10, and 8 kcal/mol, respectively). Detailed comparison is made between the structure and bonding of the silylene addition complexes with those of their carbon analogues. Significant differences, particularly in the multiple bond character of the central bond, are found.