This chapter introduces the constitutional design of a political system. It notes that although constitutions vary in the degree to which they are laid out formally, all have important informal as well as formal parts. The chapter then suggests elements that enable constitutions to be functional and enduring. Federalism and geographic centralization are introduced as issues. Federal and unitary systems are differentiated. The chapter concludes with a discussion of "constitutionalism" and a detailed examination of the British and Russian constitutions.