INTRODUCTION Originally founded to link students at Harvard University, the social networking application, Facebook, has evolved into the most visited social networking site in the world with over 90 million active users. Specializing in regional and scholastic networks, Facebook boasts an 85% market share at universities and colleges in the United States , and a recent study of more than 800 University of Florida medical students and residents determined that 44.5% use Facebook . As academic health sciences libraries explore social networking technologies to create and market library services, Facebook provides a flexible space to interface with a large number of students. Homegrown applications for Facebook have been created by libraries to answer reference questions, search online public access catalogs, and host multimedia collections. For health sciences libraries, whose users are often widely dispersed, Facebook offers several opportunities for outreach and instruction. For example, self-organizing groups of users (i.e., medical student class of 2010, pharmaceutical sciences undergraduates) afford targeted marketing opportunities despite their distributed locations (i.e., teaching hospitals, rural clinics, commercial pharmaceutical laboratories). Additionally, Facebook encourages developers to create applications that could be useful in a health sciences setting (i.e., PubMed Search application), form affinity groups (i.e., Medical Library Association Facebook group), and fashion library fan pages.