In appearance Betazoids were next to indistinguishable from humans. The only differing feature was that their irises were black. Betazoids were able to cross-breed with humans.
Betazoids were natural telepaths able to sense the thoughts and emotions of other beings and even able to influence the minds of others. Most developed their telepathy at adolescence, though a few were born with their abilities fully active. (TNG: "Tin Man") The skills varied from individual to individual based on nature ability and training. Some species, such as Ferengi, were immune to Betazoid's telepathy. (DS9: "Fascination")