This article is a sequel to my contribution entitled “When words coalesce: chunking and morphophonemic extension” in the volume The Indo-European verb (ed. H. Craig Melchert, 2012: 87–104), and intends to document cases of preverb incorporation for Proto-Indo-European (PIE). Although preverbs occurred as free morphemes with finite verbs in PIE, they could also, under conditions to be specified, undergo a change of their morphemic status from free to bound. I discuss a number of such cases and the conditions under which preverbs could undergo destressing, phonologically regular or irregular reduction, and ultimately fuse with following verbal root morphemes.