Bastian, Heiner. CY TWOMBLY: Bilder Paintings 1952-1976. Volume I. 60 pp. text, 98 color plates, 4to, boards. Berlin, Propylaen Verlag, 1978.
The first volume of an earlier catalogue raisonne project. Still an excellent reference on Twombly due to the scholarship and quality of reproductions. Text in English and German.