A recent computational study (Chaumont, A; Wipff, G. Phys. Chem. Chem. Phys. 2008, 10, 6940) showed that, in spite of their high charge and spherical shape, polyoxometalate α-PW12O403− Keggin anions PW3− can “attract each other” and form oligomers in water. This led us to speculate that these anions should also display surface-active properties, a feature supported by molecular dynamics results presented here at aqueous interfaces with an organic solvent (chloroform), with three ionic liquids (ILs) and a solid (graphite). Simulations have been performed with 20 PW3− per box and, in some cases, with different Mn+ counterions (Cs+, H3O+, H5O2+, NBu4+, Eu3+). At the chloroform interface, the highest PW3− activity (90−100%) is found with NBu4+ counterions, while with all other counterions, it is ca. 50%. The results obtained in “standard conditions” (juxtaposed solvent boxes simulated with additive potentials and TIP3P water) are confirmed with tests using either bigger boxes, SPC/E water, or a polarizable fo...