Not necessarily the best introduction for those with no base knowledge of the area (as I found out) but a thorough exploration of the origins of Gothic architecture, including key players, contemporary attitudes, and channels of influence. Focusing on Suger's Saint-Denis and the rebuilding of Chartres Cathedral, von Simson offers a detailed look at the architectural features of both as well as a careful consideration of the social and political contexts surrounding their building. Of particular interest are sections on the part played by the French crown in the development of Gothic architecture, the role of the architect in the 12th century, and the political use of historical writing by Suger. There is, however, some worrying generalisation and perhaps too liberal use of 'infallible' to describe Suger.
Overall, a rigorous and wide-ranging study of the beginnings of Gothic architecture, paying attention to specific details (even down to measurements) as well as to the landscape of political and religious uncertainty and changed that played such a key role in forming the Gothic.