With Peter Howitt, he developed the so-called "Schumpeterian paradigm", and extended the paradigm in several directions; much of the resulting work is summarised in his joint book with Howitt entitled Endogenous Growth Theory.
Tillsammans med Peter Howitt, utvecklade han det så kallade "schumpeterianska paradigmet", och utvidgade paradigmet i flera riktningar, sammanfattat i hans och Howitts bok Endogenous Growth Theory.