In this guide, transition is defined as the period of time when adolescents are moving into adulthood. This guide is designed to (a) help youth and the adults who work with them understand the role of assessment in transition and (b) describe ways to collect and use data that will lead to informed choices based on accurate assessment of each individual's assets. This guide will serve as a resource for multiple audiences within the workforce development system. It will be useful to policymakers, administrators, and a wide variety of youth service practitioners including teachers, transition coordinators, counselors, work experience coordinators, tutors, job placement specialists, and job coaches. The guide can be used in many settings including secondary and postsecondary education programs, school-to-work programs, school-to-work transition programs, One-Stop workforce centers, youth employment programs, community rehabilitation programs, and community-based organizations that serve youth and young adults, ages 14 to 25.