External quality assessment (EQA) cycles are the smallest complete units within EQA programs that laboratories can use to obtain external assessments of their performance. In each cycle, several samples are distributed to the laboratories registered for participation, and ideally, EQA programs not only cover the examination procedures but also the pre- and post-examination procedures. The properties and concentration range of measurands in individual samples are selected with regard to the intended challenge for the participants so that each sample fulfils its purpose. This aims to ensure the most significant possible information gain in every cycle using the lowest possible number of EQA samples and thus, under economically optimal conditions. Participants examine samples and the results are reported to the EQA provider, who compares them with the target values for individual measurands in every sample. The EQA provider assesses the laboratory performance, and finally communicates the assessment results to the participant. The participants evaluate the outcomes of the assessment of their examination results and can draw conclusions in the case of both failing and passing and, if necessary, define improvement measures. After completion, each cycle is evaluated by the provider so that limitations and weaknesses of the EQA program can be identified and appropriate measures taken, or to confirm its continued suitability and appropriateness.