Quillen was awarded his Ph.D. for a thesis on partial differential equations in 1964 entitled Formal Properties of Over-Determined Systems of Linear Partial Differential Equations.
Quillen ay iginawad sa kanyang Ph.D. para sa isang sanaysay sa bahagyang kaugalian equation sa 1964 may karapatan pormal na Katangian ng Over-Systems tinutukoy ng Linear Bahagyang kaugalian equation.