The C99 Standard is a version of the C programming language that was published in 1999. It introduced several new features and improvements over the previous C89 standard, including support for inline functions, variable-length arrays, and new data types like long long int. These enhancements aimed to make C more powerful and flexible for developers. Additionally, C99 improved the language's support for complex numbers and added new library functions. It also emphasized better code portability and consistency across different platforms. Overall, the C99 Standard played a significant role in the evolution of the C programming language, influencing many modern programming practices.