Citizenship by investment and residence by investment are forms of acquiring citizenship and residence due to an injection of money into a country. Born in the Caribbean, the practice of selling citizenship arrived in Europe and has sparked particular attention in the case of Malta. However, more than 20 Member States have residence by investment schemes in their legislation. In recent years, European institutions have argued against citizenship by investment, that these programs lack a genuine link, pose different risks, and should be phased out. This book seeks to answer the following question: To what extent do residency and citizenship by investment programs comply with European and international law? Using case studies, legislation, and principles of European law, analysis of case law and international courts, and national legislation from Malta and Portugal the book presents a historical overview of investment migration and an in-depth analysis of European and international Law on the subject.