In 1953/4 the Hertfordshire seat of the Earls Cowper, Panshanger, was demolished, and its important collection of continental Old Masters and British portraits was dispersed. The present article has two main concerns, one of which is to trace the formation of the collection by successive earls in the eighteenth and nineteenth centuries, in a way that reflects their evolving tastes over six generations. The other main concern is to reconstruct the house, built in the Elizabethan Gothic style by William Atkinson for the 5^th Earl at the beginning of the nineteenth century, and in particular, to reconstruct the way in which the collection was arranged and displayed. An Appendix provides a checklist of the paintings at Panshanger shortly before the death of the 7^th and last Earl Cowper in 1905, and indicates, where known, their present whereabouts.