An ASP.NET AJAX developer designs and implements web-based applications using Microsoft's ASP.NET AJAX framework. They use AJAX (Asynchronous JavaScript and XML) to create interactive web applications which can retrieve data from the server asynchronously, without interfering with the display and behavior of the existing page. They are responsible for writing clean, scalable code, debugging, troubleshooting and testing their applications. They also work closely with other team members, such as UI/UX designers and back-end developers, to integrate their work and ensure a seamless user experience. They may also be involved in requirements gathering and end-user support.