In army, there are two kinds of units; one, line unit and the other, staff unit. Line officers command the troops in the battlefield. They actually fight war. But the troops in the field are to be supplied with food, medicine, arms and ammunition, etc. These functions are performed by the staff units of the army. These do not fight in the war, but help the fighters to achieve the main purpose for which they are created.
Similarly, the chief executive in an organization has to perform various functions and also has to face a number of problems of different magnitudes. For this purpose, he must have full information about the problems which may vary from technical advice to expert opinion in different fields so as to take a right decision. In this way, having expert knowledge becomes all the more important. For this purpose, the chief executive appoints staff officers for his help. In complicated and large organizations, there exist special units of staff officers to provide expert opinion in order to facilitate the decision-making. Therefore, staff agency is an advisory organ and it plans, advises and assists.
Line agencies are concerned with the provision of services in a particular field. From top to down, a single-line authority runs downwards. They actually help accomplish the primary objectives of the organization. In our context, the functions of line agencies are performed by the field organization and they receive support from staff agencies.
Staff agencies give advice to the executive. they have no responsibility for the actual performance of the duties as line agencies are created for it. The staff is a kind of thinking, planning and advisory body, Central advisory boards Bodies are staff agencies.