We provide you with the necessary knowledge to carry out the design, execution, and evaluation of validations in microbiological testing. As a preliminary step, a general reflection is made on specific aspects of the microbiological laboratory that affect validation, such as culture media, reference strains, test procedures, etc. Practical examples are included, allowing you to learn how to estimate the uncertainty of the test method in order to comply with the requirements of UNE–EN ISO/IEC 17025:2017.