Applying for citizenship can be a complex and expensive process. For this reason, hiring an attorney can often save you money in the long run.
The N-600 is essentially an application for proof of citizenship that you already hold, as opposed to an application to become a new citizen.
Chances are that if you are a U.S. citizen you probably have one of the primary pieces of evidence listed below. However, if you are unable to locate primary evidence, know that secondary evidence may be sufficient in certain circumstances.