How Long Does My Permission Agreement Last?

Dear Rich: During my graduate research in the mid 1990's. I interviewed individuals that were appropriate and that agreed to participate in my study. I have signed and dated permissions forms that explicitly inform the participant that their recorded interview could end up in a published journal or book. Is there an expiration date on the permission they granted? 
Unless your agreement provides an expiration date ("This agreement terminates on March 2, 2017"), the permission is still valid for the purposes stated. Contract provisions may also provide a right to terminate at will or under certain circumstances (often, a set amount of notice is required)
Other reasons your agreement may have terminated. Our contracts book explains other reasons that agreements terminate:

•  Both parties have fully performed. Many contracts, particularly oral agreements, end when everybody’s done what they’re supposed to do. For example, you paid for the vintage pink mohair sweater at Etsy and the seller has delivered it. 
• One party has committed a material breach. If one party breaches, the other party can say, “That’s it, we’re done,” and terminate. 
• Court-ordered termination. Courts have the right to terminate an agreement if there was a breach, the contract was void, or the contract violates the law or public policy.
• Mutual termination. The parties to a contract are always free to mutually terminate a contract.

If none of these apply to you, your agreement is still enforceable. For more on drafting permissions, check out Getting Permission.