The main responsibility of the Acquisitions Division of the NLDSB is to build up the National Library Collection. The collection development activities consist of selection, checking, listing, ordering and acquiring of library material for the National Library.

National Library is mainly concerned on acquiring books published in Sri Lanka, books published in foreign countries on Sri Lanka and books by Sri Lankan authors.

National Library is mainly a Research and a Reference Library and is open to all members of the public. Reader Services Division is housed in three floors of the National Library. The main task of the Reader Services Division is to provide information resources to all Sri Lankans and foreigners who visit Sri Lanka, through the National Library assist them to achieve intellectual and cultural advancement supporting the national development of Sri Lanka. Reader Services Division maintains a number of services for the readers such as reference service, inquiry service, interlibrary loan service, current awareness services (CAS), selective dissemination of information (SDI), reprographic service, etc.

The main responsibility of the Bibliographic Control Division is to present information on varies publications generated in and on the country, in an organized manner for the benefit of researchers as well as general users. It provides bibliographic details (Meta data) to make users and knowledge records meet together. This includes all materials published in both print and non-print media which represent the creative and intellectual products of the nation. Compilation of the Sri Lanka National Bibliography Current, Retrospective and Cumulated volumes, Sri Lanka Periodical Article Index, Special Bibliographies pertaining to certain subjects, compilation of Directories, Indices etc. are the activities of the Bibliographic Control Division. In addition this division compiles the National Library Catalogue and National Union Catalogue, provide Cataloging In Publication (CIP) bibliographic data for authors and publishers of Sri Lanka for their publications, co-ordination of local library networks and compilation of “NATNET LANKA” newsletter.

Main role of this division is to introduce Information Technology (IT) to activities of the divisions of the NLDSB and create awareness on use of Information Communication Technology (ICT) for the activities of the divisions of the NLDSB. This division also assists other libraries in the utilization of information technology.

The role of the Conservation and Preservation Division is to conserve and preserve the numerous collections of library material in the National Library. This division also implements a number of projects in national level for the conservation of library material in other libraries in the country. In addition, this division implements the international projects such as Intangible Cultural Heritage (ICH) project, Memory of the World (MOW) programme and IFLA PAC Regional centre.

Main objective of the Library Research Division is to conduct research relevant to Library and Information Science field at national level in Sri Lanka. In addition, Library Research Division conducts workshops on Library Research Methodology for library professionals.

The role of Digital Library Division is the digital collection development of the National Digital Library. Digital collection development is carried out through various methods such as digitizing national library resources, acquisition of digital material from external sources, etc. In addition, providing digital information services to the readers and maintaining bibliographic records of digital resources is also a responsibility of this division.

Extension Services Division of the NLDSB extends its services to public, school, departmental and special libraries in Sri Lanka. Planning of library services development, advising on library matters, formulating various library standards, conducting book exhibitions, donating books for libraries, recommending library books and development of rural libraries are the main functions of the extension services division. Through these functions the extension services division aims to bring the libraries in the country to excellent information resource centers and thereby serve the nation by satisfying their information needs.

The role of the Education and Training Division is to identify the training needs of the different categories of libraries, organize and conduct In-service training programmes, seminars, workshops, lectures etc. for librarians and other library staff, awareness seminars for heads of institutions which the libraries are under them, directing and coordinating of library education activities in Sri Lanka. Through these programmes, education and training division expect to upgrade the efficiency and effectiveness of the library professionals in the country.

The role of the Publication and Book Development Division is to implement projects for the book development in the country in national level. Through these projects NLDSB expect to encourage and assist the production of quality books for the people.

Under this division of the NLDSB, publication assistance project, purchase of new publications project, editing and publishing of old classics, publishing of national library publications are implemented. NLDSB also functions as the national focal point of ISBN, ISSN and ISMN international standards numbering systems.

The aims of the Library Co-operation Division are to improve co-operation among the local libraries through various programmes, organize programmes with other libraries under Ministries and institutions relevant to the library field, and to have co-operation with the National Libraries of the world, Library Associations of the world and International Institutes in the library field such as IFLA, ALA, COMLA, UNESCO, CDNLAO, REFSALA, IASL, FID etc. and to have links with unions relevant to the library field such as government combined services librarians union, to improve the professional knowledge of the librarians and discuss their problems, maintains close relations with professional institutions in the Library and Information Science field and related fields.