This memoriam is written in memory of Robert H. Klein, Ph.D., ABPP, CGP, AGPA- DLF, who passed away this year, 2023, after contributing a lifetime of work to the field of group psychotherapy. It reviews the contributions that he made to group theory and treatment and his service to the American Group Psychotherapy Association. It concludes with an unedited email describing his thoughts about group therapy and trauma work, where he details 20 principles that group therapists should consider as they embrace group treatment to work with trauma survivors.