Computational chemistry has reached a stage of development where many chemical properties of both simple and complex systems may now be computed more accurately, more economically, or more speedily than they can be measured. Further advances in accuracy and practicality will depend on the development of both new theory and new algorithms, and mathematical techniques will play an important role in both of these areas. Improvements in computer hardware and software over the last few decades have contributed to the ability of computational and theoretical chemistry to achieve full partnership with experiment as a tool for understanding and predicting the behavior of a broad range of chemical, physical, and biological phenomena. The Nobel Prize awarded to John Pople and Walter Kohn in 1998 highlighted the importance of the advances in computational chemistry. With massively parallel computers and with the development of parallel software for efficient exploitation of these high-end computers, we can anticipate that computational chemistry will continue to change the scientific landscape throughout the new century upon which we have embarked. The impact of these advances is expected to be broad and encompassing because chemical science is central to advances in areas such as materials design, biological sciences, environmental modeling, geophysics, energy generation and utilization, nanotechnology, and chemical manufacturing.