The Blackstone’s Guide to the Borders, Citizenship, and Immigration Act 2009 provides an essential tool for understanding the important changes in border control, citizenship, and immigration law found in the Act. The Guide provides a clear explanation of developments in the acquisition of British citizenship by automatic acquisition, naturalisation and registration; the introduction of new immigration measures concerning students, children, trafficking, and other matters; and the new customs functions at UK borders and connected supervisory powers. The Guide provides a commentary that puts the new provisions into the context of existing laws, while explaining the significance of the innovations introduced. The constitutional significance of the new measures is considered, together with an emphasis on the implications of the measures for the protection of rights under the European Convention for the Protection of Human Rights and Fundamental Freedoms.