Ius doni, commonly referred to as citizenship by investment or economic citizenship, is one of the avenues of citizenship acquisition, alongside ius sanguinis, ius soli, and others. It refers to the acquisition of the status of citizenship through an exceptional (economic) contribution to the issuing country, and, by extension, a contribution to the welfare, advancement, and economic development of the host state. Ius doni is thus a specific sub-type of naturalization. The term ius doni was introduced by immigration and citizenship law specialist Dr. Christian H. Kälin, pioneer of the citizenship by investment industry, in his research on the topic. Dr. Kälin introduced the concept into the contemporary legal and political theory of citizenship by providing the first comprehensive analysis of the subject, discussing the historical, legal, and political concepts of citizenship.