This book explores how regions can thrive beyond traditional agglomeration economies by leveraging the concept of "borrowed size" -- the ability of smaller or peripheral areas to benefit from proximity to large urban centers without hosting large-scale economic activity themselves. Focusing exclusively on Japanese prefectures, the book provides comprehensive empirical analyses of how spatial interdependencies shape regional productivity, efficiency, and innovation performance. It is the first study to systematically examine the effects of borrowed size on total factor productivity convergence, productive efficiency, and regional innovation using official regional statistics, including patent indicators and other publicly available data. The book also introduces the concept of the "shadow of agglomeration," highlighting potential negative externalities associated with urban concentration. Challenging the classical understanding of agglomeration, this volume contributes a new theoretical and empirical framework for understanding regional resilience in the post-growth era. It provides robust evidence and analytical tools that will be valuable to scholars, regional planners, and policymakers seeking sustainable strategies for innovation-led regional development.