The primary interest of sandhi in Romance is as a morphological phenomenon. Adaptation of word forms to a variety of sandhi contexts gives rise to allomorphy (paradigmatic variation). Such adaptation reflects natural phonological processes which tend to reduce the markedness of sequences of phonological elements. We illustrate from Catalan and French strategies to avoid hiatus, and from Catalan and Occitan strategies to simplify consonant clusters. Romance also attests subphonemic alternations in sandhi environments, and we draw attention to cases such as intersonorant lenition of initial voiced stops in much of south-western Romance. A striking feature of Romance sandhi alternations is the readiness with which they may become morphologized or lexicalized. This outcome may arise from subsequent sound changes that make the original motivated alternation opaque, or from levelling of allomorphic alternation that makes the distribution of allomorphs opaque. We review an example of such a change in progress: the aspiration/loss of coda /s/ in Andalusian Spanish. Occasionally, a morphologized/lexicalized alternation may be (partly) remotivated, as is famously the case with rafforzamento fonosintattico ‘phonosyntactic strengthening’ in standard Italian. However, the phenomena of elision and liaison in modern French exemplify morphophonemic arbitrariness with very extensive incidence.