J A Bradney "History of Monmouthshire Vol 1, "The Skenfrith Hundreds" First published in 1904 but still a standard work.
"The Three Castles" Jeremy K Knight, Cadw, Welsh Historic Monuments, contains a short history of the early years of this lordship with detailed descriptions of the three castles. Sumptuously illustrated.
Minister's accounts for the lordship of Grosmont for the year 1257, in "South Wales and Monmouth Record Society", publications No. 3. An interpretation of the figures appears in "A year on the land in medieval Grosmont" in Gwent Local History, Number 96, Spring 2004.
"Register of Grosmont 1589 – 1812" The church registers, transcribed by J A Bradney with many footnotes – an invaluable help for family historians.
Church guide by R A Rocyn Jones, available from the church nave.
"A Survey of the Duchy Lordships in Wales 1609-1613" includes customs, description of the manor and lists of landholders; also covers, of course, the manors of Monmouth, Skenfrith and Whitecastle.
"A Grosmont Miscellany" by Philip Morgan. Notes on the social history, including the history of farming and the changes in local government. Available in local bookshops and by phone, by post or by on-line from the publishers Capella Archive at Great Malvern.
"Hidden Grosmont" by Steven Pickford, a small record of the author's probes into the unusual parts of Grosmont and its history, charmingly told with fascinating speculations. Available from local shop.
Fred G Levett: "The story of Skenfrith, Grosmont and St Maugham's" A collection of information on local parishes in 3 vols spoilt perhaps by his lack of references and by several errors; nevertheless well worth consulting . Only about 30 were printed so it is rare.
M N Jackson: "Bygone days in the March of Wales". Most details are about Skenfrith but includes some interesting notes on Grosmont
"The Battle of Grosmont, 1405: a reinterpretation", Gwent Local History, Number 97, Autumn 2004 – analyses the raid by Glyndwr's forces.
"The Grosmont Vestry in the 19th Century" - Phillip Morgan. Based on the Minutes of the Vestry and of the Parish Meetings, when they discussed secular matters.