This paper summarizes the complex unsteady, 3-D viscous flow aerodynamics (dominantly laminar) developed in flapping wing generating vortices and intersecting with them. Different flying creatures, (Insects, Birds, and Bats) flapping wing mechanisms are studied and hence being compared based on their wing kinematics and aerodynamic efficiency. The performance of low Reynolds number flyers is highly influenced by the wing shape, wing size, wing camber, aspect ratio, % camber thickness, elastic deformation, wing-beat frequency and wing twisting. The Computation technique used to analyze the wake characteristics of a flapping motion shows that the generation and shedding of vortices dominate the aerodynamic loading on the wing. The periodicity of the wing motion and the resultant vortices leads to conclude that any quantitative model must be based on unsteady aerodynamics and vortex dynamics.The preliminary assessment of the plan form and the airfoils are performed using Modified Blade Element Theory. Classical blade element theory has been successfully developed for analyzing insect wing aerodynamics, at least for the steady flow contribution. This eliminates small angle assumption and allows accurate calculation of vortex displacement velocity. The focus has been given on the study of sensitivity of the flow to the variation owing kinematics, change in wing plan form shape, airfoil shape and their distribution along the wingspan. Time-accurate Navier-Stokes solvers are employed for the preceding analysis. Even though the flow discovered in natural flyers is mainly laminar, for design perspective it is prudent to include turbulence modeling.