In this thesis I argue that, in liberal democracies, parliaments should enjoy sovereignty in constitutional decision making and I criticize the idea of judicial supremacy; this is the idea that courts should have the power to strike down legislation when they find it violates the basic values and principles of a constitutional order. After an introductory chapter where I explain the relevance and outline of my argument, in chapter two I critically examine three areas of disagreement between defenders and detractors of judicial supremacy: legal indeterminacy, the global judicialization of politics and the empirical question about the effects of courts in the protection of fundamental rights. In chapter three I tum to normative positivism in order to tie majority rule with the democratic authority of law and I also defend the desirability of judicial moral reasoning for the authority of law in liberal democracies. In chapter four I draw a line between imperfect yet full democracies and other political systems and I then use the distinction to support my argument in favour of parliamentary sovereignty in the former contexts. I also expand on what form this majoritarian democracy should take by incorporating agonistic critiques of liberalism into constitutional theory. In chapter five I develop a distinctive account of popular constitutionalism that acknowledges the legal nature of constitutions while defending popular and parliamentary sovereignty and I critically examine the relation between different forms of constitutionalism and the phenomena of populism. I conclude the thesis with a brief summary of my argument against strong judicial review of legislation.