Various programming languages can be used for Raspberry Pi GPIO (General Purpose Input/Output), including Python, C, C++, Java, and Scratch. Python is popular for its simple syntax and community support. Libraries like RPi.GPIO and GPIO Zero offer easy-to-use interfaces for controlling GPIO pins. C provides direct hardware register control and faster performance than Python. C++ and Java also provide direct hardware access to C and are suited for more complex projects. Scratch, a visual language, offers a block-based interface for GPIO pin control, ideal for beginners.