The period covered by this thesis extends from the mid- 6th/12th century to the late 8th/14th century. These centuries saw the development, maturity and apogee of Islamic architecture in Iraq as regards plan, structure and ornament. They also saw the heyday of the atabeg system, the fall of the Abbasid caliphate with the sack of Baghdad, and the establishment and decline of Mongol power. Long and comparatively peaceful reigns, such as those of the Caliphs al-Nasir and al-Mustansir, Badr al-Din Lulu' and Shaikh Uwais, generated many notable buildings. Occasionally a ruler's change of creed might affect his patronage of architecture. Thus the conversion of Badr al-Din Lulu' to Shi'ism, possibly intended as a move against the 'Adawiya sect, caused not only the conversion of many Atabikid madrasas to maqams and mashads, but also the erection of mausolea to Shi'ite imams. This thesis was undertaken in the hope of shedding light on the comparatively little-known mediaeval architecture of Iraq. The majority Of the foreign scholars who have worked in Iraq ao far have concentrated on tbe pre-Islamic past and even specialists in Islamic art have tended to concentrate on the Umayyad and early Abbasid periods. Thus there seemed to be room for a comprehena1ve work which would not only summarise the present state ot knowledge about already published buildings and their decoration but would also fill in the picture by dealing with little known and in some cases completely unpublished structures.