Mark's research interests focus on the creation of the world's first private sector during the American Revolution and the Constitutional era and the legal delineation of public and private spheres in the following decades. He has authored three books: Charity, Philanthropy, and Civility in American History (Cambridge University Press, 2002), One Nation Under Law: America's Early National Struggles to Separate Church and State (Northern Illinois University Press, 2004), and Law and Religion in American History: Private Conscience and Public Virtue (Cambridge University Press, 2016). The last book is the sixth entry in CUP's prestigious New Histories of American Law Series. Mark has also published numerous essays in academic journals and law reviews.
Mark and Blythe share a dedication to taking whatever small steps they can to improve their world during their lifetimes by protecting land from development and ensuring the continued existences of the flora and fauna that live upon it. They live with two wonderful dogs, both rescued from shelters, Lakota, a Pomeranian mix, and Archie, a Westie-Scottie mix.