Administrative law takes several froms, as agencies can act both somewhat like legislatures and somewhat like courts. They may promulgate binding regulations governing acitivites within their jurisdiction, or they may decide matters involving particular litigants on a case-by-case basis. With the modern growth of government bureaucracy, however, the rules created by executive agencies are primary legal sources with pervasive impact. In many areas, administrative law can be more immediately relevant to day-to-day legal practice than either statutory or judge-made law.
Source: Legal Research in a Nutshell, 10th Edition by Cohen and Olson
Source: Youtube