Common Table Expressions (CTEs) are temporary named result sets defined within a single SQL query. They enhance query readability and maintainability by breaking down complex queries into smaller, more manageable parts. A single query can contain multiple CTEs, each building upon the previous one. This approach is particularly helpful when dealing with intricate data transformations or calculations. Think of CTEs as reusable subqueries, but with the added benefit of being named and reusable within the same query. This modularity significantly improves the organization and understanding of complex queries, making them easier to debug and modify. For instance, if you need to calculate a running total, a series of CTEs can be used to progressively calculate the running total for each row, making the query more readable and maintainable.