Policy1-Breast (Australian Breast Cancer Screening Simulation (ABACUS)) is a continuous-time, multi-cohort micro-simulation model. It simulates the whole Australian female population over time, modelling detailed life histories of individual subjects breast cancer risk factors, life-course breast density according to menopause and hormone therapy use and, for women who develop cancer, tumour growth and detection. An extension of an earlier model of a single cohort of screening participants with breast cancer, ABACUS is a data-driven model, calibrated and validated against information from a range of sources such as cancer registries, BreastScreen service data, Medicare claims, hospitals data and cohort studies. The model has been developed under a collaboration between the University of Melbourne, Monash University, the University of New South Wales, the University of Queensland, the University of Sydney, and the Royal Womens Hospital/Royal Melbourne Hospital. We will report expected clinical and health economics outcomes (e.g cancer detection rates, screening recall and false positive screening test rates, overdiagnosis rates, quality of life measures, and incremental cost-effectiveness ratios (ICERs)) for a range of current and alternative, risk-based screening strategies. Our goal is to use the best available evidence to identify strategies that optimise health benefits while minimising costs and harms. We aim to address current key policy questions to assist decision-makers, and then operate as an ongoing resource to help evaluate new and emerging screening test technologies and to re-evaluate the role screening as the effectiveness of prevention and treatment improves.