To offer insight into how cognitive–behavioural therapy (CBT) competence is defined, measured and evaluated and to highlight ways in which the assessment of CBT competence could be further improved, the current study utilizes a qualitative methodology to examine CBT experts' (N = 19) experiences of conceptualizing and assessing the competence of CBT therapists. Semi‐structured interviews were used to explore participants' experiences of assessing the competence of CBT therapists. Interview transcripts were then analysed using interpretative phenomenological analysis in order to identify commonalities and differences in the way CBT competence is evaluated. Four superordinate themes were identified: (i) what to assess, the complex and fuzzy concept of CBT competence; (ii) how to assess CBT competence, selecting from the toolbox of assessment methods; (iii) who is best placed to assess CBT competence, expertise and independence; and (iv) pitfalls, identifying and overcoming assessment biases. Priorities for future research and ways in which the assessment of CBT competence could be further improved are discussed in light of these findings. Copyright © 2015 John Wiley & Sons, Ltd. Key Practitioner Message: A qualitative exploration of experts' experiences, opinions and recommendations for assessing the competence of CBT therapists. Semi‐structured interviews were conducted and analysed using interpretive phenomenological analysis. Themes identified shed light on (i) what to assess; (ii) how to assess; (iii) who is best placed to assess; and (iv) common pitfalls. Priorities for future research and ways in which the assessment of CBT competence could be further improved are discussed in light of these findings.