All languages have demonstratives, but their form, meaning and use vary tremendously across the languages of the world. This book presents the first large-scale analysis of demonstratives from a cross-linguistic and diachronic perspective. It is based on a representative sample of 85 languages. The first part of the book analyzes demonstratives from a synchronic point of view, examining their morphological structures, semantic features, syntactic functions, and pragmatic uses in spoken and written discourse. The second part concentrates on diachronic issues, in particular on the development of demonstratives into grammatical markers. Across languages demonstratives provide a frequent historical source for definite articles, relative and third person pronouns, nonverbal copulas, sentence connectives, directional preverbs, focus markers, expletives, and many other grammatical markers. The book describes the different mechanisms by which demonstratives grammaticalize and argues that the evolution of grammatical markers from demonstratives is crucially distinct from other cases of grammaticalization.