Event Sourcing transforms how we think about data by treating the history of events as the source of truth rather than current state. This architectural pattern provides powerful capabilities: perfect audit trails, time travel debugging, temporal queries, and the ability to reconstruct state at any point in time. Combined with CQRS, Event Sourcing enables multiple specialized projections from a single event stream, allowing different views optimized for different use cases. The pattern excels in domains with strict audit requirements, complex workflows, or where understanding causality is critical. However, it introduces complexity through storage growth, eventual consistency in projections, event versioning challenges, and a steeper learning curve. The key insight is treating time as immutable—events are facts that happened and cannot be changed, only appended to the timeline.