He is an expert in the fields of trusts and estates, comparative law, and Anglo-American legal history.
In the field of trusts and estates, Langbein is known for his scholarship advocating greater flexibility in the application of the Wills Act formalities, work which led to the adoption of the "harmless error" standard in the Uniform Probate Code.
[1] In the fields of comparative law and legal history, he is best known for his critique of the common-law jury and adversarial procedure, which he considers inferior to the Continental alternatives, especially the German system.
He has focused in particular on the history of criminal procedure, comparing the Anglo-American tradition to that of the European Continent.
His article, "The Prosecutorial Origins of Defence Counsel in the Eighteenth Century: The Appearance of Solicitors," was awarded the Sutherland Prize by the American Society for Legal History in 2000.