The term extension was first used in the United States of America in the first decade of this century to connote the extension of knowledge from the Land Grant Colleges to the farmers through the process of informal education.In India, the terms community development & extension education became more popular with the launching of Community Development Projects in 1952 & with the establishment of the National Extension Service in 1953. Since then, Community development has been regarded as a programme for an all-round development of the rural people, & extension education as the means to achieve this objective.

Extension education is an applied behavioural science, the knowledge of which is applied to bring about desirable changes in the behavioural complex of human beings usually through various strategies & programmes of change & by applying the latest scientific & technological innovations.

Extension education has now developed as a full-fledged discipline, having its own philosophy, objectives, principles, methods & techniques which must be understood by every extension worker & others connected with the rural development. It might be mentioned here that extension education, its principles, methods & techniques are applicable not only to agriculture but also to veterinary & animal husbandry, dairying, home science, health, family planning, etc. Based upon its application & use, various nomenclatures have been given to it, such as agricultural extension, veterinary & animal husbandry extension, dairy extension, home science extension, public health extension, & family planning extension.

It may, however, be mentioned here that when extension education is put into action for educating the rural people, it does not remain formal education. In that sense, there are several differences between the two. Some of these differnces are:

Objectives of extension education. The objectives of extension education are the expressions of the ends towards which our efforts are directed. In other words, an objective means a direction of movement. Before starting any programme, its objectives must be clearly stated, so that one knows where to go & what is to be achieved. The fundamental objective of extension education is the development of the people.
Agricultural extension in our country is primarily concerned with the following main objectives:
(1) The dissemination of useful & practical information relating to agriculture, including improved seeds, fertilisers, implements, pesticides, improved cultural practices, dairying, poultry, nutrition,etc.;
(2) the practical application of useful knowledge to farm & home;and
(3) thereby ultimately to improve all aspects of the life of the rural people within the framework of the national, economic & social policies involving the population as a whole.

Principles of extension education. The extension work is based upon some working principles & the knowledge of these principles is necessary for an extension worker. Some of these principles, as related to agricultural extension, are mentioned below.
1. Principle of interest & need. Extension work must be based on the needs & interests of the people. These needs & interests differ from individual to individual, from village to village, from block to block, & from state to state &, therefore, there cannot be one programme for all people.
2. Principle of cultural difference. Extension work is based on the cultural background of the people with whom the work is done. Improvement can only begin from the level of the people where they are. This means that the extension worker has to know the level of the knowledge, & the skills of the people, methods & tools used by them, their customs, traditions, beliefs, values,etc. before starting the extension programme.
3. Principle of participation. Extension helps people to help themselves. Good extension work is directed towards assisting rural families to work out their own problems rather than giving them ready-made solutions. Actual participation & experience of people in these programmes creates self-confidence in them & also they learn more by doing.
4. Principle of adaptability. People differ from each other, one group differs from another group & conditions also differ from place to place. An extension programme should be flexible, so that necessary changes can be made whenever needed, to meet the varying conditions.
5. The grass roots principle of organisation. A group of rural people in local community should sponsor extension work. The programme should fit in with the local conditions. The aim of organising the local group is to demonstrate the value of the new practices or programmes so that more & more people would participate.
6. The leadership principle. Extension work is based on the full utilisation of local leadership. The selection & training of local leaders to enable them to help to carry out extension work is essential to the success of the programme. People have more faith in local leaders & they should be used to put across a new idea so that it is accepted with the least resistance.
7. The whole-family principle. Extension work will have a better chance of sucess if the extension workers have a whole-family approach instead of piecemeal approach or seperate & unintegrated approach. Extension work is, therefore, for the whole family, i.e. for male, female & the youth.
8. Principle of co-operation. Extension is a co-operative venture. It is a joint democratic enterprise in which rural people co-operate with their village, block & state officials to pursue a common cause.
9. Principle of satisfaction. The end-product of the effort of extension teaching is the satisfaction that comes to the farmer, his wife or youngsters as the result of solving a problem, meeting a need, acquiring a new skill or some other changes in behaviour. Satisfaction is the key to sucess in extension work. "A satisfied customer is the best advertisement."
10. The evaluation principle. Extension is based upon the methods of science, & it needs constant evaluation. The effectiveness of the work is measured in terms of the changes brought about in the knowledge, skill, attitude & adoption behaviour of the people but not merely in terms of achievement of physical targets.