Database selection depends on your data structure, scalability needs, and query patterns. SQL databases like PostgreSQL and MySQL excel at structured data with complex relationships. They enforce ACID compliance for transactional integrity. NoSQL databases offer flexibility for unstructured or rapidly evolving data schemas. Document stores like MongoDB store JSON-like documents, ideal for content management systems. Key-value stores like Redis provide high-speed caching and session management. Column-family stores like Cassandra handle time-series data and large-scale analytics. Graph databases like Neo4j excel at relationship-heavy data like social networks. SQL databases support powerful JOIN operations and aggregations. NoSQL databases typically scale horizontally more easily. SQL databases have standardized query languages, making developer onboarding easier. NoSQL databases often provide better for specific use cases. Consider data consistency requirements: SQL offers strong consistency, while NoSQL often provides eventual consistency. Development speed may favor NoSQL for rapidly changing schemas. For most applications, a hybrid approach using both SQL and NoSQL optimizes for different data access patterns.