A .NET developer uses Microsoft's .NET Framework to build, deploy, and run applications. They design, develop, and test complex software systems, often involving web development, desktop applications, or mobile apps. Their work includes writing clean, scalable code using .NET programming languages, troubleshooting software issues, and enhancing existing systems. They also collaborate with other software engineers and developers to integrate .NET applications with other systems. They use tools like ASP.NET, MVC, C#, and SQL Server, ensuring optimal performance, security, and coding standards. They often participate in the entire software development lifecycle, from concept to deployment.