Though considered by some as a difficult if not impossible task or even as a challenge or a sacrilege, research on the efficacy of psychotherapy has grown steadily over the past decade. After a brief survey of the most substantial results over 40 years, the article proceeds to point out risks and misunderstandings that have arisen between researchers and clinicians. In order to illustrate this issue, two frequently used concepts in research are presented: meta-analysis and therapeutic alliance. (PsycINFO Database Record (c) 2007 APA, all rights reserved) (journal abstract)