An analysis is made of the interrelation-ship of the longitudinal parameters important to the aerodynamic design of an efficient canard or tandem wing configuration. It is shown that theoretical configuration span efficiencies substantially greater than one are feasible with the proper choice of parameters. This improvement can translate into significantly increased lift/drag ratios assuming fixed spans. The Prandtl-Munk relationship for induced drag is used as a convenient qualitative guide, with stability and trim criteria superimposed. An “aspect-ratio ratio” parameter is introduced to aid in optimizing a configuration longitudinally. It is shown that a canard/wing “aspect-ratio ratio” of approximately 3/2 to 2 is necessary to achieve peak span efficiency for a given span ratio and gap, assuming representative parameters. Large lifting tails are treated in the appendix; they are shown to be aerodynamically competitive with canards for the lower range of span ratios (<̄0.7-0.8).