The precise performance of immunohistochemical and molecular examinations of diagnostic and predictive markers is essential for the further therapy of patients. Due to the increasing number of biomarkers and their detection at the immunohistochemical and molecular level in patient tissue, the pathology has a direct influence on the therapy of patients, which increases the value of external quality assurance (EQA). In pathology, various forms are available for this purpose, such as proficiency tests. The standards of both the certification and accreditation procedures of pathology require regular participation in EQA and a statement on the EQA policy of the institutes. The quality of an EQA depends on the scientific concept, the adequate selection of material, the evaluation concept, and the communication of results.