The companies fulfill an essential mission in the vertebration of our society by the impact of its activities in the economic, social and technical fields. For the fulfillment of their objectives and the control of all the activities of their business, the companies have needed and need to document all the processes that carry out. At present, the archives of companies play an important role within the profession, their access is demanded by citizens and researchers and companies have assumed their importance from the administrative, legal and for the creation of an image to society. For these reasons, it was necessary to write a reading and consultation manual to introduce the reader to the specific nature and characteristics of company files, to provide guidelines for the organization of their documents and to answer the questions they raise the treatment of documentary series and access to information. The book is aimed at different readers. For the professional archivist, this work is a starting point for the exchange of opinions and experiences and the necessary contrast with particular situations; for the student or the opponent, a synthesis is offered on archival theory and practice within companies. For the researcher who is approaching these archives for the first time, there is an extensive list of centers in which, certainly, many research expectations are opened in the most diverse fields. For the manager and the person in charge of the companies, finally, we analyze the reasons why a file is necessary and has its reason to exist within the structure of the entity.