Constitutions come in shapes and sizes. What do we actually mean by a constitution? Does this conception encompass all fundamental legal practices and norms for organising political societies’ legal and leadership systems – commonly denoted as ‘small c constitutions’? Or are we only referring to the so-called ‘large C’ constitutions: the official, formal legally binding document that countries proclaim as ‘Constitution. This chapter explores the different concepts, definitions and elements thereof. Whatever the definition or character of the document, a constitution will have to have a higher status than other forms of written law, Hans Kelsen held, otherwise it would not be a real constitution. Does that always hold true. The chapter also discusses constitutions as a belief system, and constitutionalism.