Jurisdiction means the power of a court to try and determine a case, and to render a valid judgment. Courts-martial are courts of special and limited jurisdiction. For example, courts- martial jurisdiction applies worldwide, but is limited in application to a certain class of people— members of the armed forces. In general, three prerequisites must be met in order for courts- martial jurisdiction to vest. They are: (1) jurisdiction over the offense, (2) personal jurisdiction over the accused, and (3) a properly convened and composed court-martial. Whether a court-martial is empowered to hear a case—whether it has jurisdiction—frequently turns on issues such as the status of the accused at the time of the offense, or the status of the accused at the time of trial. These issues of courts-martial jurisdiction relate to either subject matter jurisdiction (jurisdiction over the offense) or personal jurisdiction (personal jurisdiction over the accused). Subject matter jurisdiction focuses on the nature of the offense and the status of the accused at the time of the offense. If the offense is chargeable under the Uniform Code of Military Justice (UCMJ) and the accused is a servicemember at the time the offense is committed, subject matter jurisdiction is satisfied. Personal jurisdiction, however, focuses on the time of trial: can the government court-martial him? The answer is yes, so long as the accused has proper status; i.e., that the accused is a servicemember at the time of trial.