Site Reliability Engineering (SRE) is a discipline that applies software engineering principles to infrastructure and operations challenges, originally developed at Google to manage large-scale production systems. SRE bridges the traditional divide between development and operations by treating operations as a software problem, using automation, error budgets, and service level objectives to balance the tension between releasing new features and maintaining system stability. At its core, SRE embraces calculated risk rather than pursuing perfection—availability targets like 99.9% explicitly acknowledge that some downtime is acceptable, and the remaining error budget becomes a shared resource that development and operations teams negotiate to make data-driven decisions about velocity versus reliability.