What is Commercial Law? Commercial law provides the rules that merchants and others involved in commerce must follow as they conduct business amongst themselves and with consumers. It governs the sales of goods and services, negotiable instruments, security interests, leases, principal and agent relationships, contracts of carriage, and much more. In a broad sense, commercial law also encompasses related issues like business bankruptcy and tax planning. Because various legal issues may be included or excluded from the subject of commercial law depending upon how expansively it is defined, it may be more helpful to consider the matter in terms of timing. Commercial law covers legal issues that arise prior to the initiation of a lawsuit. By contrast, once a lawsuit is filed, the same issues are more properly characterized as litigation. Thus, commercial law attorneys help their clients negotiate and enter into business deals. Litigation attorneys help their clients defend their interests in court when deals go bad.