A C# developer designs, develops, and implements applications using the C# programming language. They write clean, scalable code using .NET programming standards, identify bottlenecks and bugs, and devise solutions to these problems. They test software to ensure responsiveness and efficiency, troubleshoot, debug, and upgrade existing software, and create technical documentation for reference and reporting. They also interact with clients to understand their requirements and goals, and collaborate with internal teams to ensure software is up-to-date with the latest technologies. They play a crucial role in creating user-friendly interfaces, enhancing system performance, and maintaining code quality.