The evolution and commercialization of Web Information Systems (WIS) since 1991 has gradually shifted the focus from basic design issues to feedback analysis, visualization techniques, and agent-based negotiation support. Even during the early stages, WIS design efforts turned out to be quite substantial in scale and required a planned, managed, and structured approach. Adaptive solutions avoid redundant repetition, facilitate navigation, and increase the perceived value of provided information or services. Digital agents as proactive, goal-oriented systems promise to increase flexibility and will radically change inherent characteristics of electronic commerce. An evolution-based framework for WIS is provided and software agents are classified according to their functionality and architectural attributes into information agents, co-operation agents, and transaction agents. In this last stage of the framework, agents independently search virtual spaces and identify suitable business partners for exchanging information, collaborating in virtual organizations, negotiating contractual terms, and performing commercial transactions.