Physical and aerodynamic characteristics of a bird in flight offer benefits over typical propeller or rotor driven miniature air vehicle (MAV) locomotion designs in certain applications. A number of research groups and companies have developed flapping wing vehicles that attempt to harness these benefits. The purpose of this paper is to report different types of flapping wing miniature air vehicle designs and compare their salient characteristics. This paper is focused on mechanical design aspects of mechanisms and wings. The discussion presented will be limited to miniature-sized flapping wing air vehicles, defined as 10 to 100 g total weight. The discussion will be focused primarily on designs which have performed at least one successful test flight. This paper provides representative designs in each category, rather than providing a comprehensive listing of all existing designs. This paper will familiarize a newcomer to the field with existing designs and their distinguishing features. By studying existing designs, future designers will be able to adopt features from other successful designs. This paper also summarizes the design challenges associated with the further advancement of the field and deploying flapping wing vehicles in practice.