The chapter argues that the theory and practice of illiberalism is evolving into a new composite ideology designed for our democratic age. This ideology purports to offer a new model for the social and political order without breaking free from the master legitimating frame of our age: popular sovereignty as the ultimate source of state authority. Exploiting its normative appeal, contemporary illiberalism builds on the democratic ideal yet stretches it to the extreme. The chapter argues that to the extent illiberalism is a serious threat to constitutional democracy today, it is when illiberalism grows within such a framework: only there it is viable enough to subvert even well-established democratic regimes and achieve its ultimate goal of dismantling the liberal institutions and substituting liberal rights and freedoms with illiberal values. The chapter first surveys the multiple theoretical sources of illiberalism – from the ideological extremes of radical left and conservative right critiques of liberalism. It then outlines how illiberal regimes turn these theoretical critiques into practices of gradual erosion of liberal democratic institutions and values. After a critical take on the debates around the “illiberal democracy” concept, in the main body of the chapter the ideational core of “democratic illiberalism” is spelt out.