This is the first book-length functional-typologically inspired crosslinguistic study of comitatives and related categories such as the instrumental. On the basis of data drawn from 400 languages world-wide (covering all major phyla and areas), the authors test and revise a variety of general linguistic hypotheses about the grammar and cognitive foundations of comitatives. General linguists with an interest in case, functional typologists, grammaticalisation researchers and experts of markedness issues will value this book as an important contribution to their respective fields of interest.