This chapter reviews prognostic factors, considering those established factors in clinical use and a number of biological factors, which have been shown to be associated with clinical behaviour. The possibility of a reproducible multiparameter “intelligent” prognostic system is exciting and would provide a uniform yet personalised prediction of outcome, with reference to a large database of control patients. Nodal involvement has stood the test of time as being one of the most consistent predictors of outcome. Numerous studies have demonstrated the prognostic power of tumour stage, tumour size, and histological grade. The incidence of breast cancer is slowly increasing in most countries of the world, and the disease remains a significant cause of morbidity and mortality in populations. Artificial neural networks may provide that opportunity, allowing a set of variables relating to a patient and her tumour to be compared with a data set of known outcomes, while taking into account numerous nonlinear interrelationships between variables and control data set.