Iran's 2009 presidential election was a controversial political event and came prominently into global media focus. Alleged large-scale frauds in the election led to widespread protests which faced repressive reaction of the regime. In the absence of independent media, the story of the political upheaval was brought to the world by the protesters' extensive use of mobile phones and the Internet. This paper attempts to illuminate the role of Information and Communication Technologies (ICTs) in the aftermath of the election and in the development of the opposition Green Movement. 'Political Opportunity Structures'---the cornerstone of social movement theories - was adopted as the theoretical framework. We argue that the Internet allowed the Green Movement to enhance its political opportunities through reaching international allies and by weakening the repressive capacity of Iran's regime. Furthermore, the Green Movement used ICTs as an organizational resource to back-up demonstrations and gatherings. The ability of ICTs to promote a collective identity within the Green Movement and to create a discursive opportunity is also discussed.