One- and two-year cognitive therapy training programs are increasingly popular in the UK and overseas. Previous research has indicated that trainees show gains in competence, though this may at times be accompanied by self-doubt and stress. The present study sought specifically to gain the trainees' perspective: What happens to self-perception of competence (SPC) during cognitive therapy training – does it change over time? Do all elements of cognitive therapy skill show the same changes in SPC? Do individuals show different patterns of change? What environmental and internal factors influence changes in SPC? Twenty-four trainees on a one-year part-time training course completed a self-rated assessment of competence at six time points during the course. They also reported attributions about experiences that might have contributed to increases or decreases in SPC. Results demonstrated that SPC increases significantly over time, but there is considerable variation across different skills, and between individuals. A model developed from trainees' qualitative data indicated that the prime influences on SPC were new learning opportunities (acquiring knowledge, implementing knowledge, external evaluation, experiences with clients), self-reflection on performance, increased awareness of the standards required of a cognitive therapist, and emotional state, in particular emotionally salient memories and current stress. Practical implications of the findings for trainees, trainers and supervisors are discussed.