Abstract Ab initio MO wave functions for XHn molecules are analyzed in terms of the hybridization concept. It was found that for X from the first row (especially for carbon) the hybrid-AOs so obtained are close to orthogonal. If X is from the second row, different hybrids on the same atom overlap strongly and the well-known relations between degree of hybridization and bond angle no longer hold, although the XH-bonds-MOs are similarly well localized. Allowing for non-orthognonal hybrids the regime of validity of the hybridization concept can be extended. Musher's theory of hypervalent molecules is shown to involve implicitly non-orthogonal hybrids. Non-orthogonal hybrids can even be used to describe “stereochemically active lone pairs”, although these can also be rationalized without referring to hybridization at all. Some critical remarks concerning an overinterpretation of localized electron pairs are made.