Out of the Babel of psychotherapy models, concepts, and techniques, the therapeutic alliance stands out as a measurable phenomenon that has been shown to have a robust effect on treatment outcome. The therapeutic alliance may be a "holy grail" of psychotherapy competency because it is a validated concept that is predictive of outcome, more powerfully predictive than alternative indices, clearly defined, easily measured, and may have educational and training value. This communication reviews the concept of therapeutic alliance, the methods for measuring it, and its relationship with outcome. We also summarize the literature on how trainees acquire the ability to develop a therapeutic alliance, and evaluate the pedagogical techniques for improving trainees' skills in this area. Finally, we present recommendations for the use of therapeutic alliance measurement in residency training for competency assessment purposes, and for pedagogical approaches for improving residents' therapeutic alliance building skills.