Jean van Heijenoort was best known for his editorial work in the history of mathematical logic. I survey van Heijenoort's contributions to model-theoretic proof theory, and in particular to the falsifiability tree method. This work of van Heijenoort's is not widely known, and much of it remains unpublished.
Irving H. Anellis. "Jean van Heijenoort's contributions to proof theory and its history." Mod. Log. 2 (3) 312 - 335, April 1992.