The formal and informal organizations are inter-related. They are not mutually exclusive. There exist many informal organizations simultaneously with the formal organizations. A single formal organization like the state, the university, the industry, the church etc may consist of several informal organizations in the form of gangs, friendship groups' etc.The line separating formal and informal organization is not always clear.Any formal organization functions best when the informal organization supports it. The most orderly and efficient structure does not automatically produce a successful organizational administration if the members have no goodwill towards one another and have only personal hostilities. On the contrary, the best goodwill in the world will be insufficient for the successful pursuit of an organizational activity if the formal organization is deficient.
The most efficient and satisfactory organization is the one in which formal organization is supported the informal organization. The relationship between the formal and informal organizations is always subtle always complicated and always interesting. According to Page, the continuous interaction and association among the members of formal organization result in the emergence of informal structure of roles and relationships. He calls such informal structure consisting of primary group relations, friendships and cliques, ties of mutual obligations of aid and assistance.
According to Charles Bernard the informal organizations are necessary to the operation of formal organizations as a means of communication of cohesion and of protecting the integrity of the individual.