Sentry is an error tracking and performance monitoring platform. Developers instrument applications with Sentry SDKs, which capture exceptions, errors, and performance data. Sentry aggregates similar errors (grouping), provides context (user, session, request data), and alerts teams when critical issues occur. It's the operational backbone for application health monitoring. Sentry goes beyond simple error logging: it understands error patterns (which errors are critical?), integrates with your development workflow (create issues automatically), and provides context needed to fix problems fast (full stack trace, user session, environment).