Previous research has documented the fragmented nature of software development work. To explain this in more detail, we analyzed software developers' day-to-day information needs. We observed seventeen developers at a large software company and transcribed their activities in 90-minute sessions. We analyzed these logs for the information that developers sought, the sources that they used, and the situations that prevented information from being acquired. We identified twenty-one information types and cataloged the outcome and source when each type of information was sought. The most frequently sought information included awareness about artifacts and coworkers. The most often deferred searches included knowledge about design and program behavior, such as why code was written a particular way, what a program was supposed to do, and the cause of a program state. Developers often had to defer tasks because the only source of knowledge was unavailable coworkers.