In behavior therapy, it was only when researchers found that therapist’s variables partly explained the outcome of treatments that these variables became a topic of interest for empirical studies. However, in spite of these findings, the courses regarding the formation of behavior therapists still pay more attention to the acquisition of information, disregarding the training in relevant skills for professional competence. At this moment many behavioral treatment programs have been tested and evaluated regarding their effectiveness, but the forgotten question of therapists skills and how to train them remains unresolved in the clinical field. In order to fill this gap, the goal of the present work is to describe some relevant skills for the practice of behavior therapy with adults and children, particularly those related to the promotion of an appropriate therapeutic rapport. Some skills related to the therapeutic alliance with adults and children are presented. In addition, some significant skills for the assessment and treatment of child disorders are also described. It is expected that this work help behavior therapists working with adults and/or children to learn about some of the necessary skills to be developed in order to implement an effective therapeutic behavioral practice.