Readings and panels and autographs, oh my! We'll need a hotel to hold us all -- no, a convention center!
Of course, "the convention phenomenon" did not come about in exactly this way. It evolved along many diverse paths, and each con has its own flavor. Some focus more on books, others on media (film) or graphic novels or anime or serious literary and political discussion. I picked up an ad for "GeekGirlCon," whose goal -- loosely paraphrased -- is the support of women in all aspects of the sciences and science fiction. Cons can vary from year to year. Things can go spectacularly right, or just as spectacularly wrong, with the hotel, the guests, the organization, the programming, the economy.