It is produced by the OCLC Online Computer Library Center and includes catalog records for books, manuscripts, computer data files maps, computer programs, musical scores, films and slides, newspapers, journals, sound recordings, magazines, videotapes. WorldCat does not include book chapters or individual articles, or articles in journals, magazines, or newspapers.

From the Center for Research Libraries. Full description here. Highlights:
  –  89 journals published between 1740 and 1800
  –  Many titles from the first half of the 19th century (including more than 20 women's magazines)
  –  118 periodicals published during the Civil War (1861-1865) and Reconstruction (1865-1877) eras
  –  Trade magazines from the 19th and early 20th centuries