When traditional research methods were developed, evidence about the past was scarce and heritage repositories had to be visited in person. Human labour was required both to read and interpret sources and to create scholarly apparatus that facilitated their discovery and use. Historians now face the challenge of making sense of digital collections of sources that are so vast that they cannot be visualized or understood without computation. We describe a range of techniques that allow researchers to keep up-to-date with new information, to collect and automatically process thousands of sources, and to discover new patterns that require interpretation.