Apache Polaris is a production-grade, multi-tenant Iceberg REST catalog server built on Quarkus. It provides a REST API for catalog management (namespaces, tables, views), credential vending for cloud storage (S3, GCS, Azure), fine-grained authorization via built-in RBAC or external OPA/Ranger, and event publishing (Kafka, CloudWatch). The system supports two persistence backends: a legacy relational JDBC (PostgreSQL, H2) and a new NoSQL abstraction with custom indexing, caching, and distributed invalidation. Multi-tenancy is implemented via isolated realms, each with its own configuration and persisted state. Key entry points are the Quarkus server (`polaris-server`), a CLI admin tool, and a Python client. External dependencies include Iceberg libraries, Quarkus, Jackson, Testcontainers, and optional integrations like Open Policy Agent, Apache Ranger, and Kafka. The architecture is modular with clear SPI boundaries, making extensions (persistence, auth, federation) pluggable.