Relational databases and NoSQL databases serve different purposes in data management. Relational databases organize data into structured tables with predefined relationships and use SQL for querying, ensuring data integrity and consistency. They are ideal for applications with complex queries, such as transaction systems. In contrast, NoSQL databases offer a more flexible schema, storing data in formats like documents, key-value pairs, or graphs. This flexibility allows for horizontal scaling and quick adaptation to changing data requirements. While relational databases excel in structured environments, NoSQL databases are preferred for large, unstructured data applications like social media or big data analytics.