Squamate hemipenes have yielded much systematic data, but there have been few, if any, attempts to infer changes across the lizard–snake transition. We assess external morphology of hemipenes of major extant squamate lineages. Summarizing information across Squamata from mostly published data is challenging because of (i) patchy coverage, (ii) uncertainty as to whether described organs are fully everted or inflated, (iii) interpreting mixed text, photographs and drawings, (iv) non-standardized terminology, (v) shifting views of squamate phylogeny. However, we provide suggestions towards a unified terminology for hemipenial morphology, and score 24 lineages for 10 traits. We infer likely ancestral states as follows. (1) Ancestral toxicoferan: slightly bilobed hemipenis; simple, flared sulcus spermaticus; lack of spines; possibly flounce-like transverse flanges on body. (2) Ancestral snake: simple, flared sulcus with closely spaced, symmetrical lips; lack of spines; lack of lobular calyces; possibly unilobed hemipenis. (3) Ancestral alethinophidian: moderately to deeply bilobed hemipenis; lobular flounces; lack of spines; centripetal, bifurcate sulcus reaching tips of lobes.