A written demand telling a person or business to stop a specific action and not start it again, usually because the sender believes it violates their rights.

A cease and desist letter is often the first formal warning before a lawsuit. In intellectual property disputes, it may accuse someone of trademark infringement, copyright infringement, patent infringement, or misuse of trade secrets. For example, a business might send one after finding a confusingly similar brand name on signs, packaging, or a website. The letter usually explains what conduct must stop, why the sender believes they have legal rights, and what could happen next, such as a lawsuit, request for an injunction, or demand for damages.

Practically, these letters matter because they can change the timeline of a case fast. Ignoring one can lead to higher costs, lost evidence, or a stronger argument that the conduct was willful. Responding too quickly without legal advice can also create problems, especially if the letter asks for admissions, money, or a broad promise. In South Dakota, a cease and desist letter does not automatically create a legal deadline by itself, but it can be a step before filing in court, including claims under South Dakota's Uniform Trade Secrets Act, SDCL chapter 37-29. Like a warning sign before a sharp curve on US-14, it signals that a legal dispute may be getting serious.