Citizen orientations towards their political leaders, institutions and political systems sits at the heart of political science and political behaviour, yet despite the potential challenges distrusting citizenries pose for the operation and stability of democratic systems, there has been no consensus on what political distrust really is, what it means for the citizens that express it, what its implications are for political systems and how to best capture it across established democracies. The dissonance between empirical observations of citizen distrusting attitudes and the analytical concepts used to study political orientations, which have mainly focused on trust, make this the right time to ask “What is political distrust?” and to investigate how this attitude area can help social scientists better understand current phenomena of political behaviour across democratic systems. This thesis postulates that we cannot conclusively interpret the significance of plummeting trust indicators nor apprehend their consequences for democratic politics without a clear understanding of citizens’ political distrust, defined in its own right and separated from competing notions, such as cynicism or the lack of trust. The thesis follows a mixed methodological approach to the study of political distrust from the perspective of citizens. It develops a conceptual model for distrusting political attitudes based on theoretical work and novel empirical evidence from three European democracies – Italy, the UK and Greece. Our model conceptualises political distrust as a dynamic, relational and evaluative attitude that follows technical, ethical and interest-based assessments to judge the untrustworthiness of political agents. Further, the thesis puts this conceptual model to the test, creating a novel survey indicator and providing new quantitative evidence regarding the structure and operation of political distrust. It finds support for our conceptualisation of distrusting attitudes as retrospective and prospective evaluative judgments and highlights the prominence of perceptions of unethical political conduct in shaping political distrust. Using a multiple-item indicator tapping into evaluations of national parliament and a citizen’s preferred political party we explore the dimensionality and hierarchy of each evaluation and unravel a double operation of distrusting attitudes, both as specific assessments of political agents along these three dimensions and as a cognitive evaluative shortcut acting in a cyclical reinforcing manner. We also investigate how the newly identified aspects of political distrust relate to citizens’ behavioural intentions for participating in politics and find differences in the motivating and demotivating influence of distrusting attitudes targeted at different parts of the political system.