Process evaluations of newly developed interventions are necessary to identify effective and less effective intervention components. First aim of this study was to identify key components of a psychosocial goal management intervention from the perspective of participants, and second aim was to evaluate the intervention's fidelity. A mixed-methods approach was applied to 24 interviews with participants post-intervention and 16 audio recordings of random training sessions. Participants experienced three key components: (1) the content, in which specific exercises helped to raise awareness and (intention to) change goal management behaviour, (2) person-focused approach, specifically, the nurse as trainer and personal fit of the approach, and (3) social mechanisms, including facilitating group processes and interpersonal processes. Adherence to the protocol by the trainers was high, while differences were found in the degree to which they were able to apply the intended collaborative approach and psychological communication skills. The applied design provided valuable insights into the processes that took place. Both the effects experienced by participants in relationship to the content, approach and social mechanisms as well as the strengths and weaknesses found with regard to fidelity provide insights that can inform the development and implementation of person-focused interventions.Keywords: qualitative analysis; adaptation; arthritis; mixed-methods; behaviour change techniques Introduction Evaluating interventions in terms of the processes that have taken place has become more vital for developers and evaluators of complex health care interventions (Craig, Dieppe, Macintyre, et al., 2008). Such evaluations are necessary because they identify the effective and less effective components, and these findings can, in turn, inform future theories, intervention designs and methods (Linnan & Steckler, 2002;Michie, Johnston, Francis, Hardeman, & Eccles, 2008;Wallace, Brown, & Hilton, 2014) as well as ascertain the pathways by which an intervention's key components produce the desired benefits (Bartholomew, Parcel, Kok, Gottlieb, & Fernandez, 2011;Craig et al., 2008;Moore et al., 2014). A sound process evaluation also determines under which *Corresponding author. Email: R.Y.Arends@utwente.nl © 2016 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way. Psychology & Health, 2016 Vol. 32, No. 1, 38-60, http://dx.doi.org/10.1080/08870446.2016 conditions the intervention is effective, for whom it is effective and how it can be optimised (Craig et al., 2008;Linnan & Steckler, 2002). Especially in multicentre trials, where the same in...