Constraints in SQL are crucial for maintaining the accuracy and reliability of data within a database. They act as rules that govern the types of data that can be stored in specific columns or tables. This prevents accidental or intentional entry of incorrect data, ensuring data integrity. By defining constraints, you define the acceptable values for a column, preventing issues like storing a non-numeric value in a numeric column or entering a date that's in the future for a past-event column. Constraints are a fundamental part of relational database design, ensuring data accuracy and consistency. They can be applied to individual columns or to the entire table, providing a powerful way to enforce business rules. For example, a constraint might require a customer's email address to be unique, or a product's price to be positive.