A person's mental health and many common mental disorders are shaped by various social, economic, and physical environments operating at different stages of life. Risk factors for many common mental disorders are heavily associated with social inequalities, whereby the greater the inequality the higher the inequality in risk. The poor and disadvantaged suffer disproportionately, but those in the middle of the social gradient are also affected. It is of major importance that action is taken to improve the conditions of everyday life, beginning before birth and progressing into early childhood, older childhood and adolescence, during family building and working ages, and through to older age. Action throughout these life stages would provide opportunities for both improving population mental health, and for reducing risk of those mental disorders that are associated with social inequalities. As mental disorders are fundamentally linked to a number of other physical health conditions, these actions would also reduce inequalities in physical health and improve health overall. Action needs to be universal: across the whole of society and proportionate to need. Policy-making at all levels of governance and across sectors can make a positive difference.