This book presents a collection of papers on a series of exploratory studies on the rise and fall of downtowns (Downtown Dynamics), which the author's group has been working on with the aim of constructing an artificial society that contributes to the planning and management of crowds by developing Agent-Based Social Simulation (ABSS). In particular, the book includes (1) an analysis of 20 years' worth of survey data on visitors' shopping-around behavior for Osu district in Nagoya city, as a representative Japanese downtown, (2) correlation analyses of spatial distributions between Visibility Graph Analysis (VGA) as a "visibility index" and crowding in middle scale urban spaces, (3)agent modeling of visitors' shopping-around behavior and construction of the Downtown Dynamics Model as an artificial society, and (4) modeling of the vision-driven agent as a "crowd generator" and its applicability to spatial design and sign layout in urban spaces.