He is known primarily for his writings on literary history, particularly his attempts to fuse the studies of literature and of culture; in the former area he expanded upon, and in part questioned, the idea of "race, milieu, and moment" as described by Hippolyte Taine.
He also contributed a great deal to the study of pedagogy, arguing for the pedagogical importance of the explication de texte, the French predecessor of close reading.
Among his shorter works is a still-authoritative 1892 life of the French poet Nicolas Boileau-Despreaux in the series Les Grands Ecrivains Francais.
Lanson proposed the idea of "literary sociology," a complex formulation of the relationship between social influences on an author, readers' expectations, and the text.
In the era of the New Criticism, with its interest in the exploration of metaphor and image and the distancing of a text from the circumstances that created it, Lanson was seen as a pedant obsessed with historical and biological trivia and a rigid and unliterary philology.