Acquisition Through Exchange:

Acquisition through exchange is another mechanism by which Collection Development can take place. Of course, it goes without saying that the library should have material (like duplicates or publications of its own or of the parent body) that can be exchanged. The United State Book Exchanges established in 1948 acts as a pool for participating libraries who want to dispose of their duplicate materials of value to get in return other materials which they do not possess. Other examples of organisations facilitating exchange are Medical Library Association, American Association of Law Libraries, American Theological Library Association and Unesco's Library Division. As a mater of fact, the Unesco Bulletin for Libraries (when it was existing) used to have a section listing the materials available on an exchange basis from foreign libraries. 

Acquisition Through Purchase:

Since the library cannot build its collection purely on the basis of gifts and exchanges, acquisition by purchase becomes inevitable. But no library can purchase all relevant documents owing to limitation of financial resources. Therefore, it becomes necessary to make a judicious selection of all documents considered relevant to the library before purchasing them. It is here that Ranganathan's Five Laws of Library Science and Principles of Book Selection come in handy. It is assumed here that the librarian has acquired the necessary knowledge and skill to select the best documents for the library concerned. In regard to acquisition by purchase, a number of methods are followed by libraries. They are: 

1)  Tender system 

2)  Quotation method 

3)  Direct ordering with publishers 

4)  Standing vendor method 

5)  Dealer Library Plan (DLP) 

6)  Standing order 

7)  Books-on-approval 

8)  Open purchases