Web interfaces challenge traditional definitions of usability. A three phase model for website evaluation is proposed, based on initial attractiveness, exploration/navigation and transaction. Usabilityis rede fined as trade-o. between increasing the user’s motivation to encourage exploration and purchasing in e-commerce, and the costs of usability errors. Heuristics for assessing the attractiveness of web user interfaces are proposed based on aesthetic design, general arousal created bycontent, corporate identityand brand, and the perceived utilitymatc hed to users’ requirements. The heuristics are tested byev aluating three airline websites to demonstrate how different attractiveness and traditional usabilitytrade-offs contribute to overall effectiveness.