The goal of science is to accumulate knowledge that answers questions such as “How do things work?” and “Why do they work that way?” Scientists use a variety of methodologies to describe, predict, and explain natural phenomena. These methods are so diverse that it is difficult to define a unique scientific method, although all scientific methodologies share the assumption of repeatability (Hempel & Oppenheim, 1948; Kuhn, 1962; Popper, 1934; Salmon, 1989). In this chapter, we first briefly review why replications are highly valued but rarely published. Then we describe a collaborative effort—the Reproducibility Project—to estimate the rate and predictors of reproducibility in psychological science. Finally, we detail how we are conducting this project as a large-scale, distributed, open collaboration. A description of the procedures and challenges may assist and inspire other teams to conduct similar projects in other areas of science.