This diploma thesis deals with quality management systems in conformity with ISO 9001:2008. In the first part, we briefly describe the development of management systems from their initial phase (organization of labour division) to the quality management systems as we know them today. A brief description of the areas which are important for the establishment and the maintenance of a certified or of an uncertified quality management system will follow. In the second part, the quality management system of an electrical engineering company is presented first, followed by the presentation of a chosen construction company. Finally, a comparison of both quality management systems is made based on the quality manuals prepared by the companies. The findings show that considerable differences in quality management occur especially at the implementation stage: the scope of the certification with respect to the scope of the work, the number of connections between the processes and their documentation, especially in the documents of the second and lower stages.