This is a quantitative study into real executive-coaching relationships to determine the ‘active ingredients’ which contribute to the effectiveness of executive coaching. The study focused on the so called ‘common factors’ of coaching conversations, i.e. those aspects which are non-specific and unrelated to coaching technique, approach or philosophy, such as working alliance, self-efficacy of the client, personality of the client, and personality match between client and coach. Data collected from 156 client-coach pairs participating in formally contracted, external executive coaching, was analyzed to examine the impact on coaching outcome of client self-efficacy, personality and personality matching in terms of MBTI-profiles, coach interventions and client-coach relationship. Strong indications were found for the prediction of coaching outcome by (1) the coaching relationship as a working alliance, as experienced by the client; (2) the self-efficacy of the client; and (3) generalized coaching technique as experienced by the client.