The core skill of a clinical and forensic psychology practice on which to base the ongoing engagement and treatment of offenders is the use of assessment. A forensic psychologist uses assessment to gather reliable data on the characteristics of the offender and the offense they have committed in order to develop relevant intervention and treatment strategies. The authors note, however, that many clinicians do not use offense assessment as part of their work with offenders. The authors suggest that knowledge of the offense is important to understanding the offender and developing successful treatment strategies. This paper presents a draft protocol for an index offense analysis guide developed for use in forensic psychology practices. The benefits of this guide have been demonstrated through pilot programs instituted with prisoners and patients in secure settings. An anonymous case is presented as an example of the successful use of the guide. References and appendix