To compare and contrast institutional theories used in organizational analysis, the theoretical frameworks and arguments of leading contributors to institutional theory are reviewed and recent empirical studies using institutional arguments are examined. Both approaches reveal considerable variation in the types of concepts and arguments employed, and it is argued that further improvement and growth in institutional theory is dependent upon analysts dealing more explicitly with these differences. In addition, the relation between institutions and interests is explored to show that institutional features of organizational environments shape both the goals and means of actors. Attention is called to the two primary types of actors shaping institutional environments in modern societies--the state and professional bodies--and to the way in which their interests and mode of action shape institutional patterns and mechanisms.