Some bar associations and attorney organizations offer certifications, including certification of lawyers in the field of personal injury. Certification is not required to practice personal injury law, but may help a lawyer demonstrate knowledge in the field to potential clients. Within the U.S., not all state bars offer certification for personal injury law. Some states, such as New Jersey, allow lawyers to become Certified Trial Attorneys, a credential that is available to both plaintiff and defense attorneys. Some states, such as Arizona, restrict the use of the words "specialist" or "specialize" to lawyers who have obtained a certification from the State Bar Board of Legal Specialization in a specific field of law, with one such certification being in the area of personal injury law.