Abstract: Recently, interest has been directed to small autonomous flying vehicles, largely motivated by the need for aerial reconnaissance robots inside buildings and confined spaces. In military and commercial fields, there are similarpotential demands for such micro-air vehicles (MAVs). Thelinear dimension of the intended MAVs ranges from 10 cm to 1 cm or even smaller. At such a size, the fixed- or rotary wing aerodynamic configuration would not work because the Reynolds number (Re) of the wing is so low that enough lift and control forces could not be produced. Novel aerodynamic configuration must be sought. However, there already exist such autonomous MAVs in nature: the insects. In the design of small flying machines, it would be very helpful to understand first how these small animals fly. In this article, we review recentachievements in the field of insect flight aerodynamics. We first summarize the kinematics of the flapping motion of insects. Next we present issues related to the unsteady lift mechanisms of flapping wings of the fruit fly and similar insects. Then we discuss the lift (and thrust) and power requirements of hovering and forward flight in the fruit fly. Recent work on insects with two pairs of wings is also discussed.