The Abbey Church of St Leonard of Old Warden is a Grade I listed church in Old Warden, Bedfordshire, England. It became a listed building on 31 October 1966.
St Leonard's is named for Leonard of Noblac and dates to the early 12th century but the present structure is predominantly 13th century, with 14th, 15th and 16th century additions. The base of the tower, including the tower arch, is 12th century Norman, with the remainder rebuilt in the 15th century. The church was considerably reworked in the mid and late 19th century when the elaborate wooden interior was added. The church is built mainly of brown cobblestones with limestone dressings, with some later working in red brick and in coursed limestone. The south porch was built in 1952 to a design by Professor Richardson and is timber framed with red brick infill and a gabled tiled roof. It was added in 1952 by Mrs Dorothy Shuttleworth in memory of her son, Richard Ormonde Shuttleworth (1909-1940).
Today the church is best known for the richly ornate wooden carvings with which it was "beautified" by the Rt. Hon. Robert Henley-Ongley, 3rd Baron Ongley of Old Warden in the mid 19th century. From widely differing periods and mostly from Belgium, France and Italy, the carvings are said to include a number of panels removed from the private chapel of Anne of Cleves; these can be identified by the initials AC surmounted by a crown. A number of wooden panels including 15 showing Biblical scenes were stolen from the church in 1997 and were never recovered. It is intended to replace them with contemporary carvings of a similar nature.
A noted feature of the church is the medieval stained glass of the 14th century in the north wall which was originally in nearby Wardon Abbey and which shows the figure of St Margaret on the right holding a rope while on the left is a figure of an Abbot of Wardon Abbey in the white habit of a Cistercian. Further along the north wall in the chancel is a marble tablet by Goscombe John dedicated in memory of Frank Shuttleworth (1845-1913) by his widow, Mrs Dorothy Shuttleworth. Some of the inscription was erased later to record that their only son Pilot Officer Richard Ormonde Shuttleworth RAFVR was killed in a flying accident during World War II while serving in the RAF. The lectern bears the eagle and motto of the Royal Air Force and was given by Mrs Shuttleworth again in memory of her son.