The paper introduces Tropos, an agent-oriented software development methodology designed to build agent-oriented software systems. Tropos is based on two key ideas: using agent and mentalistic notions throughout all phases of software development and emphasizing early requirements analysis to deeply understand the environment and interactions between software and human agents. The methodology is illustrated through a case study of the eCulture system, a web-based broker of cultural information and services for the government of Trentino. The Tropos language for conceptual modeling is formalized using UML class diagrams. The paper outlines the five main development phases—Early Requirements, Late Requirements, Architectural Design, Detailed Design, and Implementation—and defines key concepts such as actors, goals, plans, resources, dependencies, capabilities, and beliefs. It also describes the modeling activities, including actor modeling, dependency modeling, goal modeling, and capability modeling. The detailed design phase specifies agents' micro-level details, and the implementation phase uses the JACK Intelligent Agents platform to realize the system. The paper concludes with a discussion of the development process, which involves analyzing goals on behalf of different actors using a non-deterministic concurrent algorithm.The paper introduces Tropos, an agent-oriented software development methodology designed to build agent-oriented software systems. Tropos is based on two key ideas: using agent and mentalistic notions throughout all phases of software development and emphasizing early requirements analysis to deeply understand the environment and interactions between software and human agents. The methodology is illustrated through a case study of the eCulture system, a web-based broker of cultural information and services for the government of Trentino. The Tropos language for conceptual modeling is formalized using UML class diagrams. The paper outlines the five main development phases—Early Requirements, Late Requirements, Architectural Design, Detailed Design, and Implementation—and defines key concepts such as actors, goals, plans, resources, dependencies, capabilities, and beliefs. It also describes the modeling activities, including actor modeling, dependency modeling, goal modeling, and capability modeling. The detailed design phase specifies agents' micro-level details, and the implementation phase uses the JACK Intelligent Agents platform to realize the system. The paper concludes with a discussion of the development process, which involves analyzing goals on behalf of different actors using a non-deterministic concurrent algorithm.