Liberty is of vital importance that every individual should possess it as much as possible. In this respect, liberty refers to the ability individuals have to control their own actions. However, different concepts about liberty show the position of individuals in the society. These concepts are mainly based on the social and political contexts. In the political context, liberty is a tranquility opinion based on the mind arising from the opinion about the notion of each person’s safety. To have this liberty, the government must be constituted in such a way that one man need is not afraid of other. Relative to the social context, liberty pertains to the freedom provided by the government. It entails one’s right to be free from any unnecessary restraint of the government. In addition, liberty should enable one to pursue his/her personal desires and interests that are free of any improper interference from the government. In this paper, we evaluate the similarities and differences between Montesquieu’s ideas of political liberty and Constant’s account of modern liberty.