A Microsoft IIS Developer primarily focuses on designing and managing applications for Microsoft's Internet Information Services (IIS), a web server application and set of feature extension modules created by Microsoft. They are responsible for the development and implementation of applications, ensuring their compatibility with IIS, optimizing server performance, and managing security settings. Additionally, they troubleshoot issues, maintain updates, and integrate other Microsoft technologies such as ASP.NET. They also collaborate with other team members to create efficient web environments, requiring a strong understanding of web protocols, server diagnostic techniques, and coding languages such as HTML, CSS, and JavaScript.