Falsifiability is a cornerstone of science. It states that scientific claims---propositions, hypotheses, theories---must be testable by experiment. A scientific claim is falsified if an empirical test contradicts it; if a claim withstands repeated attempts at falsification, it is accepted as fact. This article discusses three examples of falsified theories about software. They address the reliability of multi-version programs, the prediction of program bugs by means of software metrics, and the advantages of software models (UML). These examples demonstrate how falsifiability can eliminate incorrect theories and help reorient research and practice.