Better than the jacket blurb you'll find by following the link is this excerpt from the preface by U.S. Supreme Court Justice Stephen G. Breyer:
This book ... helps us understand how law among nations and beyond single nations develops through cross-referencing, through efforts to harmonize, and through the creation of hybrid rules of substance and procedure. It helps us understand where this law develops, regionally or internationally. And it helps us understand the significance of the temporal leads and lags created as this law develops over time. In a word, the book helps us understand, talk about, and evaluate what is happening before our eyes.