Container registries are centralized repositories for storing, managing, and distributing container images, serving as the critical bridge between image builds and deployments. These registries implement the OCI Distribution Specification, ensuring interoperability across tools and platforms while providing features like access control, vulnerability scanning, image signing, and geo-replication. Whether using public registries like Docker Hub or private registries like ECR and Harbor, understanding authentication methods, tagging strategies, and lifecycle management is essential for secure and efficient container operations. A key insight: always reference images by digest rather than tags in production to guarantee immutable deployments, and leverage pull-through caches to avoid rate limits and reduce latency.