Focusing on whether the United States court system is effective in resolving conflicts and disputes, this article begins by summarizing research conducted involving mediation assessment. The authors argue that increased court use of alternative dispute resolution processes coincided with a substantial number of studies concerning the success of this resolution process. After detailing what is known about mediation processes, outcomes, and successes, the authors describe the development of the assessment mediation process, utilizing both objective and subjective knowledge, begun in 1995 with the Mediators Skills Project (MSP). The Assessment of Mediation Process and Successful Outcome (MPSO) instrument discussed in this article is one of the practitioner-oriented products of the MSP. After describing the process and outcome dimensions of the MPSO, the authors explain the ways in which the MPSO instrument was tested for both reliability and validity. The authors contend that testing results indicate that the MPSO is an assessment instrument that can easily evaluate the effectiveness of mediation because the Likert-type format is easy for individuals to complete and the length of the instrument is not prohibitive. The authors further contend that the MPSO provides valid and reliable assessments of the multiple process goals and final outcome dimensions important in assessing mediation effectiveness. References