If the United States is a nation of immigrants, as stated by a famous definition, it has not been always ready to welcome people coming from different shores. Policies of inclusion have been replaced, at times, by regulations intended to keep out foreigners considered inadequate to be part of the body of the nation. This volume, the product of a collective research work, explores the policies on immigration both for the principles they promote and for the contradictions they expose, touching upon sensitive current topics of discussion. In order to make the reasoning even more complete, the authors and the editor have decided to complement the texts with documents and tables that can contribute to make even clearer the general guidelines of US policy toward immigration.