This book constitutes the documentation of the results achieved within a proirity program on spatial cognition established by the German Science Foundation (DFG) in 1996 involving 13 research groups in Germany and leading scientists from abroad. The 22 revised full papers included were first presented during a colloquium in fall 1997 and then went through a second round of thorough reviewing. The book is organized into three parts on spatial knowledge acquisition and spatial memory, formal and linguistic models, and navigation in real and virtual worlds. All in all the book is a unique report on the state-of-the art in the interdisciplinary research field of spatial cognition and its potential applications.