The Master of Library and Information Science (MLIS), also referred to as the Master of Library and Information Studies, is the master's degree that is required for most professional librarian positions in the United States. The MLIS is a relatively recent degree; an older and still common degree designation for librarians to acquire is the Master of Library Science (MLS), or Master of Science in Library Science (MSLS) degree. According to the American Library Association (ALA), "The master’s degree in library and information studies is frequently referred to as the MLS; however, ALA-accredited degrees have various names such as Master of Information Studies, Master of Arts, Master of Librarianship, Master of Library and Information Studies, or Master of Science. The degree name is determined by the program. The [ALA] Committee for Accreditation evaluates programs based on their adherence to the Standards for Accreditation of Master's Programs in Library and Information Studies, not based on the name of the degree."

Admission to MLIS, programs normally require holding a bachelor's degree in any academic discipline and library schools encourage applications from people with diverse academic backgrounds.

In the United Kingdom, it is more common for a vocational degree in library and information science to bear the standard designation MA or MSc. In most Commonwealth universities, bachelor's and master's programs have been merged to create the MLIS/MLISc degree. IFLA committees have discussed global standards for librarian credentials.

In Canada, ALA-accredited schools of library and information science sometimes grant MI (Master of Information) degrees, though some institutions retain the designation "MLIS" or "MISt". However, regardless of the name of the degree conferred, virtually every school of library and information studies in Canada comprises programming for library science, information science, archives, and museum studies.