Presents an obituary for Yvonne M. Agazarian (1929-2017). Agazarian was a brilliant theoretician, clinician, and teacher who devoted her life to the development of a theory of living human systems (TLHS) and its systems-centered therapy and training (SCT). Her work is best known in group psychotherapy because her theory integrated general systems theory and Kurt Lewin's work and created a common language to bridge group dynamics and psychoanalysis. Quite uncommonly, she formulated theoretical constructs and operational definitions that translated her theory into methods and techniques so that every intervention tested the validity of the theory and the reliability of its practice. (PsycINFO Database Record (c) 2019 APA, all rights reserved).