When Martin Luther nailed 95 criticisms of the Catholic Church to the door of his local church in 1517 he sparked not just a religious Reformation, but an unending cycle of political, social and economic change that continues to this day. By challenging the authority of the Pope, Luther inadvertently unleashed a revolutionary force: the power of the individual to determine his or her own thoughts and actions. Over four centuries later, the Protestant minister Martin Luther King Jr was acting on the same revolutionary principle when he rejected racial discrimination and spearheaded the US Civil Rights Movement. The legacy of the Reformation is all around us, influencing our work life, our family life, even our sex life, as well as our political views and sense of national identity. From literature to science, from gay marriage to the 'War on Terror', a vibrant struggle for Protestant principles is alive in Britain, America and the developing world. This is the story of the Reformation and its lasting legacy - in effect, how Protestantism created the modern world.