There is a worldwide movement towards alternatives to judicial decision-making for legal disputes. In the domain of criminal sentencing, in Western countries more than 95 % of cases are guilty pleas, with many being decided by negotiations over charges and pleas, rather than a decision being made after a judge or jury has heard all relevant evidence in a trial. Because decisions are being made, and people incarcerated on the basis of negotiations, it is important that such negotiations be just and fair. In this paper we discuss issues of fairness in plea-bargaining and how we can develop systems to support the process of plea and charge negotiation. We discuss how we are using Toulmin’s theory of argumentation and Lodder and Zeleznikow’s model of online dispute resolution to develop just plea bargaining systems. A specific investigation of the process of charge mentions is discussed.