The organization is the carrier of human survival，life and development，but also the tool and result of knowing and changing the world. In various types of social organizations，Informal Organization often goes with Formal Organization，and also is the inevitable result of organizational members of interaction in the workplace in the long-term. The theory of informal organization composed of thoughts and academic viewpoint of management，is an indispensable component to the system of organization theory. In 1934，Roethlisberger and Dickson，major participants in Hawthorne Experiment，they initially and formally put forward the new concept of “Informal Organization” in “Management and the Worker：Technical vs. Social Organization in an Industrial Plant”，based on summarizing the research process and conclusion of Hawthorne Experiment，and expounded the real meaning of the Informal Organization to “limit production”and the non-logical reasons of works’ behavior，thereupon then，they created the theory of informal organization. After that，the most influential two monographs：Barnard published “The Functions of The Executive”in 1938，Roethlisberger and Dickson Co-published “Management and the Worker” in 1939，which founded the basic content of informal organization theory. Follow-up researchers promoted the development and evolution of informal organization theory based on group dynamics，interpersonal relationship and social network theory. However，there was some misunderstanding in domestic academic circles in the process of introducing the theory of informal organization，and Chinese scholars had not a systematical and profound study on operating rules of Informal Organization，the interactive model between Informal Organization and Formal Organization，organization of lacks the thorough system research a long time，which brought about the recessivation phenomenon of practice value of informal organization theory. For this purpose，systematically research on informal organization theory，and clarify domestic academic circles understanding of the informal organization theory and its practical values，which is necessary to improve the level of organization management.

In this book，informal organization theory as the research object，this includes not only combing，summarizing and analyzing systematically domestic and international informal organization theory，but also deepening and supplementing core contents of informal organization theory. Therefore，this book conducts the systematic research on informal organization theory from the following four aspects：

Firstly，this book combed and summarized the basic process of development and evolution of informal organization theory. This book analyzed the management background and its theoretical origin about informal organization theory，tested the academic study process on the concept of informal organization proposed in detail，summarized specific contribution to the development of informal organization theory by Roethlisberger，Dickson，Barnard made，clarified the basic context of development and evolution of informal organization theory. Then，this book analyzed in-depth some historical misunderstandings produced in the process of introducing informal organizations theory from abroad，discriminated Informal Organization from other related concepts，initially made a comparative study of informal organization theory between enterprises and public organizations.

Secondly，in order to reveal deep-root reasons of the spontaneous formation of Informal Organizations，verify the non-logical reasons determined and influenced the individual behavior and attitudes by Informal Organization，this book systematically discussed origins，structure features and internal operation rules of Informal Organization，constructed the evolution model of Informal Organization. Thus，it deepened the core content of informal organization theory.

Thirdly，according to the relationship between interdependence and mutual restriction of Informal Organization and Formal Organization，and comparing the fundamental differences of the two，this book systematically studied four kinds of interactive modes：antagonism，restriction，auxiliary and fusion of these between Informal Organization and Formal Organization in management practice，so then，improved and perfected theoretical contents of interaction in between the two.

Fourthly，in view of specific operation dilemmas during informal organization theory transformed into practical values in domestic management practice，this book proposed and compared concepts of recessivation and explicitation of informal organization theory in organizational management practice，furthermore，discoursed upon the specific visual methods and some explicitation measures to discriminate and develop Informal Organization.

In this book，in order to achieve the academic innovation from the following aspects：

Firstly，this book corrected some misunderstandings on the generation of Informal Organization concept in domestic academic circles，and clarified the confusion and deviation in defining the concept of Informal Organization.

Secondly，this book analyzed the theoretical origins of the informal organization theory，and tried to explore differences in informal organization theory between enterprises and public organizations.

Thirdly，in the light of studies on origins and internal operation characteristics of Informal Organization，and relationships of interdependence and mutual influence between Informal Organization and Formal Organization，the author built the development and evolution mode of Informal Organization.

Forthly，according to practical awkward dilemma that hard to manage Informal Organization publicly and operationally，this book proposed concepts of recessivation and explicitation of informal organization theory from the angle of organizational management practice，furthermore，initially explored some open and exercisable measures to realize the explicitation of informal organization theory，in order to understand profoundly the practical value and application of informal organization theory.

Keywords：Organization；Formal Organization；Informal Organization；Explicitation