It has become orthodox to criticize Charles I for his failure as a politician. Such criticism is both accurate and anachronistic. It fails to appreciate that for Charles the business of kingship was not the art of politics but the pursuit of conscience. Charles took to heart his father's injunctions to follow conscience and he obeyed them rigidly. Through the study of speeches, letters and royal prayers this essay examines the centrality of conscience to Charles I's kingship. It shows how the divisions of the 1640s led him temporarily to abandon conscience, and finally it studies the king's self-construction as the conscience of the commonwealth – the central stance of the Eikon Basilike.