By combining different aspects of auditing and by focusing on the individual auditor and observing auditors at work, this dissertation explores the auditing concept. It focuses on activities carried out by auditors in local settings and how the macro-level phenomenon of “auditing” is realised in micro-level, day-to-day audit work. In doing this, the following research question is addressed: What does the auditor do? The dissertation includes and discusses certain aspects of auditing. The aspects chosen provide certain opportunities and limitations and are as follows: the audit profession, audit quality, auditing standards, structure versus judgment, the production of comfort, expert systems and trust versus scepticism. The empirical material consists of observations and interviews. The findings suggest that from an auditor perspective auditing includes not only a professional side but also a more commercial side. It appears that auditors combine more traditional tasks such as quality assuring the client’s information and reporting with tasks more directed towards assuring that the client firms’ management is satisfied. The findings also suggests that from an auditor perspective audit quality is about comfort and that making structured judgments seems to be an important action towards reaching a sufficient level of comfort and, hence, to perform high-quality audits. Finally, the findings of this dissertation suggest that much of the “professionalism” in the audit profession lies with the audit firms. Substantial knowledge is “built in” to the audit firm system; an important auditor skill is to be able to operate the system whilst appearance, behaviour and conduct is about adhering to such effort and auditors are influenced by audit firm expectations on how audit work should be done. The consequences of such “audit firmalization”, a concept identified in this dissertation, on the audit profession seem to be an important focus for future research.