Most U.S. states will recognize a Non-Compete Agreement as a valid, enforceable legal document, which means that the parties in the agreement are bound to its terms and conditions.
However, some states do not recognize non-compete agreements at all, so it's important to check your state laws to determine if your state recognizes this document.
In addition, if you are trying to enforce a non-compete clause or agreement from another state in a state where a non-compete is not recognized, chances are it will not be valid.
The terms of the non-compete must also be reasonable.
As an example, if you worked at a telecom provider and they included a clause in your Employment Contract that said you couldn't work for a competing provider for a certain amount of time, that might be considered reasonable if you were a top-level executive with access to lots of imformation about the company, such as business plans or financial information. However, even in that case, if the contract said that you would be unable to work in the telecom industry at all if you left the company, that could be considered an unreasonable term and would likely be difficult to enforce.