Book excerpt: This book is address to the students of GAP and ADE degrees. It contains the two following subjects: Contracts and Companies (GAP) and Commercial Law (ADE). And it adjusts perfectly to the requirements of its study exigences, 100%. That is the reason why it follows an unusual order among mercantilists, since it brings together content that usually appears in different volumes. Thus, students will have in their hands all the theoretical content of the subject, and it will be essential for them whether they follow the subject physically attending classes or remotely, through the virtual modality of the GAP degree. The study plans for these degrees have minimal legal content, I would even say ridiculous. At GAP they do study law in other subjects, but only public law, never private. That is why the manual begins with an introductory topic 1 on the historical origin and concept of commercial law. The topic is explained at length because it is essential and would not be understood otherwise. Topic 2, on the concept