--- - |2 Abstract Little is known about the mechanisms underlying how interviewers establish and monitor baselines of respondent behaviour. This study addresses this knowledge gap by characterising the practice of establishing baselines and measuring the accuracy of interviewer judgements based on assessments of baseline and departure behaviours. Eighteen professional interviewers viewed two videos of naturalistic interviews, reported the cues they perceived as informative for establishing and assessing a baseline, and diagnosed respondents' internal states. Participants reported multiple cue types as informative, but predominantly relied on non‐verbal cues. Overall, participants were sensitive to 27% of respondents' identified internal states but showed improvement over time. They achieved a hit rate of 20% during early interview stages and a hit rate of 33% during late stages. Although non‐verbal cues dominated reports, attending to verbal cues afforded participants greater efficiency in identifying respondent internal states. Implications and recommendations for practice are discussed. - 'Journal of Investigative Psychology and Offender Profiling, Volume 16, Issue 2, Page 138-149, June 2019. '