Dewey's Principle:

Melvil Dewey's principle states: "The best reading for the largest number at the least cost" According to this principle a library should select, within the financial resources available, the best documents which may satisfy the information needs of the maximum number of readers. The term "best" is relative. It means a document which "may be the best in its own field, the best that will be read, the bet, of which good use will be made, the best that will answer certain demands". The best documents are those which satisfy the just demands of the users for recreation, knowledge and study; the documents which cater to the social and cultural needs of the users. A classic or a masterpiece may not be in demand for the time being, but it is the best book to be selected for its literary worth and for its use to the coming generations. The second part of Dewey's principle - for the largest numbers - refers to the users of the library and their information needs,  specified or unspecified. Our selection of documents should be such as to satisfy as many readers as possible, the limitation of resources notwithstanding. This is possible when we know our readers and their reading needs.  

The last part of the principle at the least cost - reminds us that the book budget of a library is never enough  to meet all  the  information needs of the users.  The concessional  rates, acquisition of documents by gift and exchange, are some of the methods to save the limited funds for more purchases. The  suggestion is that whatsoever is to be bought must be bought, but with an eye on strict economy. At the same time it should be seen that this economy does not result in the development of a poor book collection consisting of cheap books by incompetent authors. The principle expects us to be careful in our selection and economical in our purchases to ensure optimum satisfaction to the maximum number of our readers.