Tropos is an agent-oriented development methodology based on knowledge-level concepts (such as actor, goal, and the dependency between actors) with a particular focus on requirements analysis. This paper presents a pattern language for guiding developers, especially those without previous Tropos experience, through the various design challenges faced when using Tropos. The patterns format allows us to motivate the modelling constructs, justify each of the development stages, and address specific modelling problems. These patterns are inter-linked in such a way that developers can navigate from higher-level to lower-level patterns as they apply the Tropos methodology. The paper has two goals: to motivate the use of agent-oriented methodologies such as Tropos to a wider set of developers, and to provide guidance for the different development activities of the Tropos methodology. Specifically, we focus on the development stages, models, and diagrams of Tropos. The patterns in this paper cover the early and late requirements analysis stages.