Hendricks's work deals with modern mathematical and philosophical logic and concentrates primarily on bringing mainstream and formal approaches to epistemology together — from epistemic reliabilism, counterfactual epistemology and contextualism to epistemic logic, formal learning theory and what is called 'modal operator epistemology'. Modal operator epistemology, developed first by Hendricks in "The Convergence of Scientific Knowledge" (Dordrecht: Springer, 2001), since developed further in a number of papers and books – see in particular "Mainstream and Formal Epistemology" (New York: Cambridge University Press, 2006, winner of CHOICE Outstanding Academic Title 2006) – is the cocktail obtained by mixing alethic, tense and epistemic logic with elements from formal learning theory in order to study the limiting validity of convergent knowledge.