A no-trespass letter provides important written documentation warning someone to stay off property that you own or control. The letter could serve as evidence for law enforcement officials, if the matter escalates into an official investigation. No-trespass letters are issued for a variety of reasons, including warning against unauthorised hunting or fishing on rural property, or using a vacant lot as a playground. No-trespass letters often follow verbal warnings and are meant to show that you are serious about the issue.

Gather details documenting the trespassing, such as photographs or eyewitness testimony. Obtain addresses of the trespassers, if possible. For example, it's fairly easy to obtain the address of a neighbour trespassing on your property.

Address the letter to a specific person, or a parent or guardian, if the person is under 18. Get to the point in the first paragraph by informing the recipient that property you own at a certain address is private, and that no trespassing is allowed. In the next paragraph state that you have proof that the person has trespassed on your property and that the activity is unacceptable.

Write in the third paragraph that the letter serves as a formal warning that future acts of trespassing may lead to an investigation by police. Send the letter by certified mail to confirm delivery.