Periodicals Index Online currently indexes over 15 million articles
going as far back as 1665 and every article in each journal is indexed, from
volume 1 issue 1 to recent times. If PIO indexes a publication, it is indexed back to its first issue and through approximately 1995 (or its last date of publication), subject to periodic updating. Every year, PIO adds records for more than one million new articles. This retrospective coverage makes it possible to readily and quickly search through extensive back runs of journals (not just the last 10 or 20 years as many electronic indexes offer).
PIO's scope is international and includes journals in English, German, Italian, French, Spanish and other Western languages. Some monographic series are also included. The focus of PCI is on publications produced throughout the twentieth century; those beginning in the eighteenth and nineteenth centuries which continue into the twentieth are indexed from their inception. PIO covers not only journals published by academic presses, but also those journals published as popular reading which now provide valuable research materials for scholars. See a
complete list of journal titles indexed by PIO.
