Rate constants for bimolecular reactions, obtained through time-resolved kinetic studies both in the gas and liquid phases are reviewed. Data for reactions of MeSiH, PhSiH, ClSiH, SiCl₂, SiMe₂, MeSiPh, SiPh₂ and SiMes₂ are covered. Where possible, substituent effects relative to SiH₂ have been obtained. These demonstrate widely varying effects between different types of reaction, which aids mechanistic understanding. Reactivities are high for all silylenes, but substituents can reduce them by both electronic and steric effects. The gas and liquid phase data (mainly for SiMe₂) are compared and appear to be reasonably consistent. This review, although detailed, is not comprehensive.