Walking in Abruzzo (Cicerone, various editions) — the standard English-language hiking guide to the region, covering routes in the Gran Sasso e Monti della Laga National Park including approaches to the Corno Grande. The Club Alpino Italiano also publishes detailed Italian-language guides to the Gran Sasso massif.
Italian Ways by Tim Parks — Parks travels Italy by train and takes in the country's textures, rhythms, and contradictions. Not about Abruzzo specifically, but gives a sharp and affectionate account of Italian life and landscape that sharpens the eye for everything you see here.
The Albergo Diffuso — the model pioneered at Santo Stefano di Sessanio has been written about widely in Italian architecture and rural-development literature. Daniele Kihlgren's project has been covered in Italian newspapers and international design press; searching his name alongside "Santo Stefano" turns up substantial background reading.
Christ Stopped at Eboli by Carlo Levi — set in Basilicata rather than Abruzzo, but essential reading for understanding the rural south of Italy that the albergo diffuso project was working against: the isolation, the abandonment, the gap between the Italian state and its mountain villages. Published in 1945, still startlingly vivid.