This book offers a dynamic introduction to the new developments on national security review of foreign direct investment (FDI) from the perspectives of both domestic law and international investment law. COVID-19 and the Russian invasion of Ukraine have intensified FDI screening to an unprecedented scale, yet its purposes, scope and potential impact remain ambiguous and controversial. The book first attests the legitimacy of FDI screening by using the theory of National Security Constitution. Part I explicates the national security, public order and public health exceptions clauses in international investment law and the novel EU Regulation on FDI screening. Part II provides an in-depth analysis of FDI screening in China, France, Germany, Italy, the Netherlands, Poland and the UK, which have either witnessed momentous changes in domestic law recently or have adopted new laws to cope with the growing security concerns. The book illustrates how States and the EU are using legal instruments to tackle exigent and emerging challenges and the complexity of national security emanated from foreign investment, in the context of evolving disruptive digital technologies and the structural change of the global economy. The volume will be of great value to a wide range of audiences including academics in investment and trade law, legal practitioners, in-house counsels, policymakers, business professionals and law and business students at the graduate level.