Shadowcliff, also known as the Fellowship of Reconciliation Headquarters, is a historic home located at Upper Nyack, Rockland County, New York. It was built in 1921, and is a large two-story, Classical Revival style masonry dwelling. The 44-room residence features three porticoes, Palladian windows, and has a clay tile roof. It has housed the headquarters of the Fellowship of Reconciliation since 1957.
It was listed on the National Register of Historic Places in 2014.