An administrative law judge is a judge who oversees an administrative agency, and who makes decisions that the agency is responsible for. When the federal government or state governments create certain programs, they also create agencies to oversee some of these programs, and to be responsible for enforcing the laws, resolving disputes, and interpreting legislation. Examples of such agencies include the Equal Opportunity Employment Commission, the Worker's Compensation System, and the Environmental Protection Agency. An administrative law judge works within these agencies to resolve disputes or to interpret law.
Administrative law is the branch of US Law that regulates government agencies. Each agency is vested with power by the government that creates it. In other words, the government delegates certain powers to the agency, and may also determine the appropriate structure of the particular agency.
If the administrative agency has to interpret laws or resolve disputes, someone, or a group of people, needs to be in charge of doing this. The government may specify who is in charge of mediating disputes, ruling on issues, and/or interpreting the meaning of laws. Alternatively, the agency may set up its own internal governing structure.
Often, regardless of who set up the specific structure, the relevant administrative agency will have one more more administrative law judges. An administrative law judge will thus function as a leader within the agency. When people violate the laws the agency is designed to protect, or when there is an issue regarding the meaning of one of those laws, the case will be argued in front of the administrative law judge.
For example, if you have a dispute with your employer's insurer about a worker's compensation claim, in many jurisdictions, the Worker's Compensation Board is vested with the authority to oversee this dispute. Some states have a panel of one or more people to hear the argument between the injured employee and the insurer. Other states assign the case to an administrative law judge, who will hear the arguments that both sides make and determine whether they are right.
If there is a question about the meaning of a law that an agency has the authority to enforce, the administrative law judge will also address that concern, and clarify the legislation. For example, equal opportunity laws prohibit discrimination. An administrative law judge on the board of the Equal Opportunity Employment Commission can hear cases in which it is unclear whether an employer's actions fall under the definition of illegal discrimination. The administrative law judge can make a decision and interpret the law in order to determine whether the discrimination was prohibited.