SQLAlchemy is a widely-used Python library that provides a high-level interface for interacting with relational databases. It serves as an Object-Relational Mapping (ORM) tool, allowing developers to work with database tables and records as Python objects.

With SQLAlchemy, developers can define database models as Python classes, where each class represents a table in the database. These models can define relationships between tables, such as one-to-one, one-to-many, or many-to-many relationships. SQLAlchemy offers a powerful querying API that enables developers to retrieve, update, and delete records from the database using Python syntax, which is then translated into SQL queries.

In addition to its ORM capabilities, SQLAlchemy also provides a core SQL expression language, allowing developers to write SQL queries directly when needed. This offers flexibility for complex queries or scenarios where ORM operations might be insufficient.

Overall, SQLAlchemy simplifies database interactions in Python applications by providing a high-level, intuitive API, supporting multiple database backends, and offering advanced features for handling database relationships and transactions.