Negotiation skills are essential in everyday life, whether in a professional or personal context. Negotiation enables two parties to address misunderstandings and avoid conflicts through an exchange that depends as much on the interpersonal skills of the negotiators as the tactics employed. Acquiring these skills requires not only sound conceptual knowledge but also practice and mentoring. This paper describes the BiLAT game-based simulation and tutoring system developed to provide students, initially United States Army soldiers, with an environment to practice preparing for and conducting bilateral negotiations. We describe the models that were created to implement BiLAT, with a particular focus on the challenge of designing for and tutoring in the ill-defined domain of negotiation. An initial assessment of the training effectiveness of the system indicates significant situation-judgment gains by novices.