Unlike economic theories of tax law enforcement, real income tax law application requires thorough interpretation of the law and the actual facts with regard to tax purposes. The automatic assessment produced by a computer program in German tax offices suggests the existence of a mechanically operated taxation akin to a weaving mill. However, empirical studies of tax administrations in the USA, the Netherlands, and Switzerland, as well as examinations carried out by the German Courts of Audit shed light on a subjective information revealing and decision making process. Unfortunately, the German tax administration does not provide individual tax assessment and tax compliance data which could be empirically analysed in comparison with the findings from abroad. Empirical economic studies are required to answer the question of how the German income tax law is applied. Thus, an expert questionnaire was developed and successfully pre-tested in tax offices with the aim of encouraging a nationwide study. A research proposal suggested interviewing tax advisers on their professional experience with tax offices. The German Federal Ministry of Finance initiated an online survey addressed to the tax advisers. The study and its results are critically reviewed with regard to methodology, previous insights, and the earlier proposal.