Publishing agencies fall under three broad categories:

i)  Trade Publishing Houses /Companies, Booksellers and Others; they publish 

• books of all varieties; 
• periodicals and serials; 
• bibliographical publications such as indexing publications, abstracting publications, reviews, etc. 

ii)  Not-for-Profit Publishers: Learned  societies, professional bodies, etc. These publishing agencies concentrate on publishing 

• Scholarly and research journals 
• Conference proceedings 
• Technical reports. 

iii)  Government  agencies: Ministries, Departments, Directorates, and  such  other agencies: .Government is a very major publisher today; all  varieties of documents such as books,  monographs,  reports, periodicals, serials,  and secondary  publications  are brought out by government agencies and institutions. 

Among these categories of publishing agencies, trade publishers are the ones who are very active in promoting their sales, through advertisements, issue of catalogues and bibliographies, announcement bulletins, leaflets,  folders, etc. Information about newly published books, forthcoming publications  in a variety of subjects keep constantly flowing into libraries. In fact, this flood of announcements, catalogues and folders, etc., pose a problem to libraries, not only because of their bulk and weeding work involved but also because of the paucity of time to scarf them. Publishers specialise in subject areas such as medicine, science and technology, law, arts, music, etc. and bring out books for special groups - children's' books; textbooks for schools and colleges; paperbacks, reference books, reprints of out-of-print books and such other. The publishing trade is thus well organised and information about books published and to be published flows systematically and regularly into libraries.

There is a well established rapport between the book trade and libraries and hence collection building in this area operates satisfactorily. In the case of materials published by learned societies, professional associations, etc., libraries have to establish regular contacts with them by becoming institutional members, to  be on their mailing lists  to  get information about their publications, exhibitions, etc., organised by professional bodies to keep track of their publishing activities. As there is  no organised system operating collectively for publications of these bodies selection and acquisition  of  materials published by these bodies poses problems for libraries. Government publications are among the  most difficult areas in  collection development. By its  very  nature, the government set up is a slow machinery; very often it operates without any time schedule, particularly in its  publication  work. Announcements of new publications, catalogues and special lists do come out, but without the necessary speed to market them, particularly in countries like India. But these publications are of immense value for special and academic libraries. Therefore special efforts are necessary to keep track of government publications.