This chapter highlights some of the most commonly used theoretical frameworks in the field of counseling and psychotherapy, and discusses their application in the Relational Equine-Partnered Counseling (REPC) approach to equine-assisted counseling and psychotherapy (EACP). The REPC approach is intended to be trans-theoretical, enabling therapists of diverse clinical orientations to integrate REPC into their EACP practice. The chapter presents an overview of each highlighted theory and its integration in EACP. These theories include Psychoanalytic, Adlerian/Individual Psychology, Person-Centered, Behavioral, Cognitive-Behavioral, Gestalt, Existential, Choice Theory and Reality Therapy, Constructivism, and Family Systems.