The bicarbonate/chloride exchanger band 3 (Anion Exchanger 1, AE1) is the most abundant protein in the erythrocyte membrane, it has an important role in gas exchange and functions as a point of attachment for the cytoskeletons maintaining the mechanistic and osmotic properties of the erythrocyte. Band 3 is found in three distinct protein complexes within the erythrocyte membrane: an ankyrin-dependent tetrameric band 3 complex, a dimeric band 3 complex bound to the protein 4.1-GPC junctional complex and as freely diffusing dimeric band 3 complexes. Much if not all of our present knowledge of these protein complexes is derived from mouse knockout model systems and human variant blood samples. This review will explore what is known about the band 3 complexes of mice and humans, focussing on the observed species differences and their potential functional consequences.