This book examines labour regulation and labour mobility in two professional baseball leagues: Major League Baseball (MLB) in the United States and Nippon Professional Baseball (NPB) in Japan. Through vivd comparative study, this book explores how each league internally regulates labour mobility and his internal regulation engages with external regulation from the legislature, statutory authorities and the courts. This comparison of two highly restrictive labour markets utilizes regulatory theory and labour regulation and suggests a framework for a global player transfer system in baseball.