Comparison is central to most work in linguistics. But what do linguists compare when they compare languages? Do different levels of linguistic description require their own specific units of comparison? Does the aim and scope of the linguistic description bear any relevance to their choice - or can the same units be used in different linguistic subdisciplines? These are the key questions this book tries to answer. It is not a book about 'contrastive analysis' as a distinctive branch of linguistics, but about comparison in linguistics in general. It is about the analytical apparatus used by linguists and whether this allows comparisons to be made across languages. Among the central concepts treated are semantic primes, pragmatic functions, and basic word order. The ten chapters are grouped in four sections (derivational morphology, syntax, semantics and pragmatics, and discourse studies) and cover a broad spectrum of linguistic disciplines, ranging from contrastive linguistics and linguistic typology to translation studies and historical linguistics.