A library is a place where information resources are collected, organized, and made available to users. Libraries tend to collect material that is produced outside the organization or institution that houses the library. Libraries are often quite formal, and follow nationally or internationally standardized ways of organizing materials.
A documentation centre functions in a similar way to a library, but often also collects (and sometimes produces) documentation on the activities of the organization or institution where it is located. Documentation centres often have a sectoral focus: for example, you may find "Agricultural Documentation Centres" or "Co-operative Documentation Centres", which try to collect all relevant information produced by and about that sector.
A resource centre performs many of the same functions as libraries and documentation centres, but usually has a strong community focus. In addition to producing, collecting, organizing and distributing information in a number of formats, a resource centre may serve as a meeting place, a communication centre, a venue for workshops, a referral centre or direct service provider, an advocacy centre, and sometimes a cultural museum.From Certificate in Managing NGO Resource Centres. Edited by Sue Adams. Coady International Institute, St. Francis Xavier University, 2003.