If you are of a certain age, you may remember in the distant past a peculiar method for looking up magazine articles that might seem alien to today's young people. As I recall, a teacher would lead the class down to the school library and present the students with a seemingly impossible task: finding magazine articles about a certain person, event, or subject. Those of us who were paying attention at that moment would wonder how the teacher expected us to accomplish this task. Everyone knew that, though magazines would be likely to run stories about news events around the time that the event happened, for the most part, we'd have to flip through all of the years of all of the magazines to figure out when an article was written about a specific topic.
Then came the big revelation: the school librarian would show us a a set of big, thick books (they were bound in red at my library) that would tell us the names of magazines that had published articles about a certain topic in a given year, and in which issue and on what page we could find the article. A whole year! That meant that all we had to do was select a range of years, look up a person, event, or, really, anything else from each year, and write down the title, date, and page numbers of the magazine that we needed to find.
That series of books, as many of you may recall, was the Readers' Guide to Periodical Literature. Though it wasn't the first periodical index, nor has it ever been the most comprehensive, it seems to be the one most stuck in the memories of people who come to the Magazines and Newspapers reference desk looking for old magazine articles. I think that the reason for this is indicated in the title -- the "Readers' Guide" serves, unlike more subject-specific periodical indexes, a broad audience of readers rather than a small group of researchers. You won't find indexing for Living Reviews in Relativity in the Readers' Guide, but you will find Time. And while you won't find any references to the Annals of the Association of American Geographers here, you will certainly see citations for National Geographic.
In short, the Reader's Guide has long provided access to the stuff that 95% of readers want 95% of the time, which has made it a mainstay in public and school libraries for the last hundred years, which is why most of us above the age of, say, twenty, have probably come across it at least once in our lives.
The library also has the Reader's Guide Retrospective in our collection of databases, which means that users can electronically access indexing to popular American magazines from 1890 up to 1982. This is quite a boon to historical researchers, particularly because this is the only indexing available for many of these titles, which provides important contemporary perspectives on the events of the 20th century.
However, if you have a chance, stop by the Magazines and Newspapers Center and see if you can remember how to use the index that introduced so many young people to the principles of periodical research.