Computational chemistry is the branch of theoretical chemistry whose major goals are to create efficient computer programs that calculate the properties of molecules (such as total energy, dipole moment, vibrational frequencies) and to apply these programs to concrete chemical objects. It is also sometimes used to cover the areas of overlap between computer science and chemistry. Computational chemistry methods are being developed & utilized to quantitatively characterize molecular components & interactions at a local (ligand-receptor) scale. Deterministic and stochastic system process analysis & optimization techniques, are applied towards elucidation of larger network structures (interlinked signaling, regulatory & metabolic pathways). The latter process relies on interpretation of data from network perturbation experiments, that may include consideration of genetic perturbations, environmental perturbations and disease state. Meanwhile, a great deal of software development activity is being expended on the software firms' core computational chemistry programs. Indeed, new versions of many flagship software packages have just been released, and they & some entirely new programs are bringing new levels of capability, flexibility, speed & accuracy to the application of the technology.