This report presents the results of the archaeological investigation carried out by Archaeology South-East at Stanmer House, Stanmer, West Sussex between May to August 2011. The fieldwork was commissioned by ABIR architects in advance of construction of a new rear wing to the house, within the footprint of the northern wing demolished in the 1960's. The excavations have revealed evidence of three primary phases of development at the house. These include evidence of a late 16th or 17th century building, additions to this structure of the late 17th of early 18th century, and the construction of a substantial 'L' shaped service wing of the period of rebuild of the property by Henry Pelham II and Dubois (1721 - 1725). Later periods of more minor modification and addition to these structures have also been traced.