Are you talking about a living will? These are documents that set forth your wishes if you are unable to make medical decisions on your own and often names someone to make those decisions for you if you are unable. If this is what you are talking about the answer is yes and such a product is often adequate.
If you are talking about a true trust - such as leaving something of value (stocks, bonds, money, etc.) in trust for a minor or elderly person the answer is still yes they are recognized but be VERY careful. If you are talking about a true trust - you should see an attorney who specializes in trusts. They can be very tricky and there are many pitfalls.
Best of luck to you.
