This study explores the flow structures and unsteady force generation mechanisms of a flapping-wing micro air vehicle 'DelFly Micro' in forward flight configuration. Stereoscopic Particle Image Velocimetry (Stereo-PIV) measurements were performed to acquire three dimensional flow fields in the wake. Six components of forces and moments were captured simultaneously by use of a miniature force sensor. (C) 2015 The Authors. Published by Elsevier Ltd.