Starting tomorrow (2007-01-01), ISBNs (International Standard Book Numbers) will be 13 digits long instead of 10. Basically, they'll add "978" to the beginning and calculate the check digit differently. This way, they'll fit into the EAN (International Article Number) scheme. This also prepares for the event of ISBN shortages for certain prefixes; these can then be issued ISBN-13s starting with 979-.
Also, I hope I manage to sleep despite the fireworks here.