An ActiveRecord developer designs, builds, and maintains database-driven applications. Their work involves creating data models and associations, managing transactions, and implementing validations. They utilize the ActiveRecord library, a part of the Ruby on Rails framework, which automates mapping between classes and database tables. This enables CRUD (Create, Read, Update, Delete) operations on database entries. They also handle complex queries, optimize database performance, and ensure data integrity. They work closely with other developers to integrate their work into larger applications while adhering to best coding practices. They also troubleshoot and resolve any issues related to database interactions.