This image depicts a dorsal view of an adult, Cimex lectularius bed bug. Adult bed bugs are on average 5 mm long, oval-shaped and dorso-ventrally flattened. Like other members of the order, Hemiptera, they possess piercing-sucking mouthparts. Adults are brachypterous; the hindwings are nearly absent and the forewings are reduced to small, leathery pads. As you can see here, nymphs look like smaller, paler versions of the adults. (from CDC PHIL library, Image# 12704)
Image and Description courtesy of CDC Public Health Image Library - (CDC-DPDx; Blaine Mathison)