Columbia subject headings:
Information services--Canada--Directories.
Information services--United States--Directories.
Special libraries--Canada--Directories.
Special libraries--United States--Directories.
Speical libraries--United States--Directories.
Harvard subject headings:
Information services--Canada--Directories.
Information services--United States--Directories
Special libraries--Canada--Directories.
Special libraries--United States--Directories.
Princeton subject headings:
Directories.
Information services--Canada--Directories.
Information services--United States--Directories.
Special libraries--Canada--Directories.
Special libraries--United States--Directories.