Serendipity, the process of finding something of value initially unsought, has played a prominent role in modern science and technology. These "happy accidents" have spawned new fields of science, broken intellectual and technological barriers, and furnished countless products that have altered the course of human history. In the realm of patent law, one curious aspect of accidental discoveries that has received little attention in the academic literature and the courts is how they mesh with the substantive law of invention. This Essay shows that applying conventional doctrines to accidental inventions is theoretically untenable and, in certain circumstances, may result in unfortunate outcomes for the inventor. As a result, this Essay offers an alternative approach that is better suited to deal with accidental inventions. Finally, this Essay reflects on how accidental inventions benefit the patent system and the public, especially their potential to spur significant follow-on innovation.