Outsourcing and offshoring lead to a rapid influx of new developers in software projects. That, in turn, manifests in lower productivity and project delays. To address this common problem we study how the developers become fluent in software projects. We found that developer productivity in terms of number of tasks per month increases with project tenure and plateaus within a few months in three small and medium projects and it takes up to 12 months in a large project. When adjusted for the task difficulty, developer productivity did not plateau but continued to increase over the entire three year measurement interval. We also discovered that tasks vary according to their importance(centrality) to a project. The increase in task centrality along four dimensions: customer, system-wide, team, and future impact was approximately linear over the entire period. By studying developer fluency we contribute by determining dimensions along which developer expertise is acquired, finding ways to...