This article focuses on recent scanning tunnelling microscopy studies
that have led to an improved understanding of the interaction of hydro
gen with silicon surfaces. The structure and bonding of the Si(111)-7
x 7 and Si(100)-2 x 1 surfaces are described together with the adsorpt
ion and desorption of hydrogen from these surfaces. The role of hydrog
en in the passivation of silicon surfaces and silicon chemical vapour
deposition are also discussed.