Throughout the 20th century, the interest of several areas in International Relations has increased. Professionals and researchers in History, Law, Political Science, Sociology, Economics and many other scientific areas have realized that International Relations is a fertile field for academic investigation, offering multiple possibilities to observe and analyze international politics as well as a country’s foreign policies. Thus, this book gives the reader an opportunity to get to know the main authors that best represent the field of International Relations and offers them the chance to understand how the perspectives of other scientific fields influence the philosophical and theoretical approach on international relations studies.