The main issue in the development of agent-based architectures for E-Commerce applications is to produce specifications that describe precisely the functional and temporal properties of agents and their roles. An agent should be able to dynamically change its behavior according to the context of its collaboration. Interactions among agents must remain secure and consistent with E-Commerce business rules. Formal modeling, and analysis of agent-based architectures promote understanding and reasoning on these issues. This paper presents a theory of agents, and a formal description of an E-Commerce architecture. The visual and formal descriptions are complementary,leading to validation and verification prior to committing to an implementation.