This paper examines, both theoretically and experimentally, the possibility of improving the aerodynamic characteristics of a biplane configuration by adding winglets. Theoretical calculations show good agreement with experiment in predicting inviscid drag due to lift. Theoretical and experimental results indicate that the addition of winglets to an optimized biplane configuration can increase the ideal efficiency factor by up to 13%, as well as increasing the lift-curve slope and maximum lift coefficient. A theoretical analysis comparing the biplane with an optimized winglet to an equivalent monoplane indicates that the biplane has the potential for a 6.4% increase in L/Dmsa[ and a 13% increase in CL/CD, the classical endurance parameter.