The field of library science has been changing in the last two decades. Some of the changes have resulted from innovations in technology; others have come about in response to changing needs of the community and of patrons. Advances in information storage and retrieval have enabled libraries to provide more varied information in less time, but have also strained the budgets of many libraries. Shifting centers and characteristics of the population have forced some public libraries to expand and modify services at a rapid rate, while other libraries have seen declines in the number of patrons.