Book excerpt: This book constitutes the refereed proceedings of the International Conference on Spatial Information Theory, COSIT'95, held near Vienna, Austria, in September 1995. Spatial Information Theory brings together three fields of research of paramount importance for geographic information systems technology, namely spatial reasoning, representation of space, and human understanding of space. The book contains 36 fully revised papers selected from a total of 78 submissions and gives a comprehensive state-of-the-art report on this exciting multidisciplinary - and highly interdisciplinary - area of research and development.