In order to analyze “freedom of expression” as one of the basic rights of the people, one needs to know the subject of “expression”; in the sense of what “expression” is and what its functions and characteristics are. Considering the key elements of message, sender, receiver and channel, it is important to recognize the key element between them. In addition, in order to provide a proportionate analysis of “freedom of expression” in the cognitive and legal system of Islam, the approaches to freedom of expression and its philosophical foundations such as the principle of “independence”, “human dignity”, “the market of ideas”, “the right to determine one’s destiny”, “the value of safety”, “the slippery slope” and the like are discussed. Also, in Islamic literature, an attempt has been made -by presenting a report on the propositions that mention the objectives, to examine the value of expression and the station of listening and choosing and the functions of freedom of expression in eliminating and prohibiting oppression and tyranny. Also, the legislative evidence of freedom of expression has an important place in this analysis. In order to understand the nature of freedom of expression, it should be identified first and the elements of this right, including the rightful, the object of right, and its unsubstantial issues, should be discussed. Freedom of expression as a social matter and in the form of political law, will only have its function when its relationship with the government is determined based on the government’s supportive policy. This right has its limits and guarantees of implementations, proving that without the detailed analysis, this basic institution in the social structure cannot be used.