(750-892AD) Descending from Al-Abbass, the uncle of the Prophet Muhammed (pbuh), these Abbassid emirs established the second major Islamic dynasty under which Muslim Caliphate reached its highest development. As efforts of spreading Islam receded, these Emirs embarked on an enlightenment mission consisting essentially of the spread of knowledge and elaboration of technical and artistic works. The Abbassids became patrons of a number of gigantic construction projects extending from large mosques and complex palaces to large-scale urban design and city planning and consequently they played a fundamental role in the development of city planning and its architecture. This article examines major architectural and urban works of this dynasty highlighting their main innovative signs. It starts with a brief historical background on the socio-political changes they introduced, then explores their major architectural and urban achievement. Finally, a summary of the key innovative elements of Abbassids' architecture is given.