The notion "word" is investigated cross-linguistically in a series of studies systematically comparing lexical representation and processing in English, Polish, Arabic, and Mandarin Chinese, using a variety of priming techniques. The studies so far reveal considerable diversity, with languages differing widely in types of lexical organisation. Mandarin appears to rely primarily on non-combinatorial representations, while English and Polish employ in addition a decompositional, morphemically based system. The non-concatenative morphology of Arabic is also highly combinatorial, and plays an obligatory morpho-phonological structural role. We find little evidence for specific cross-linguistic constraints on lexical structure and content.