A key aspect of knowledge work is the analysis and manipulation of sets of related documents. We conducted interviews with 12 patent examiners and 12 scientists and found that all face difficulties using specialized tools for managing text from multiple documents across interconnected activities, including searching, collecting, annotating, organizing, writing and reviewing, while manually tracking their provenance. We introduce Passages, interactive objects that reify text selections and can then be manipulated, reused, and shared across multiple tools. Passages directly supports the above-listed activities as well as fluid transitions among them. Two user studies show that participants found Passages both elegant and powerful, facilitating their work practices and enabling greater reuse and novel strategies for analyzing and composing documents. We argue that Passages offers a general approach applicable to a wide variety of text-based interactions.