The present article explores how liberalism and modern thoughts entered Iran and how they influenced political thought and institutions in contemporary Iran. It also briefly considers how Iran's traditional religious and historical discourse addressed modernity and liberal constitutional theories that were distinct from its own. During most of the past 150 years, the traditional discourse regarded modernity and liberalism to be "the other." Some of these thinkers rejected modernity and liberalism entirely, others attempted to discriminate between good and bad elements of modernity and liberalism, and took account of the good, while rejecting the bad. A few adopted both liberalism and modernity wholeheartedly. Each of these assessments generated new or revised strands of political thought in Iran. In the end, liberalism failed to attract sufficient support to sustain itself, but indirectly affected Iranian politics through refinements in earlier traditional and religious political discourse and by placing Iran's governance on constitutional foundations.