Several books provide big history' accounts of the origin of the current world, and one may wonder how much value further work of this kind can add. Harari in my view succeeds through two fascinating volumes on the history and possible future of humankind, drawing on interpretations of research in a wide range of disciplines. Sapiens traces key step-changes in human evolution, starting with how the cognitive revolution around 70,000 BCE enabled language and common beliefs or fictions' that could foster large-scale cooperation and collective action. Religion, paper money or political organizations such as states are all figments of human imagination, and ultimately have no meaningful independent existence. Yet, supported by human beliefs they can enable homo sapiens to eradicate other species, sustain a vibrant capitalist economy, and wage war. Technological change starting with the agricultural revolution has enabled massive growth in human populations and the human conquest of the physical world. Homo Deus examines where humanity might be headed in the future, and the focus is more on posing questions and dilemmas rather identifying particular scenarios as more or less likely. Harari starts off on a very optimistic note, remarking how many of the major problems that have plagued humanity through history such as war and premature death from disease have been largely solved. Although serious challenges such as climate change remain, they can at in principle be solved through technological and social change. Humans even have the potential to become godlike and amortal, with the ability to extend their expected lifespan and use genetic modification and artificial implants to enhance their physical and mental capacities. But good news often raises new challenges. A recurrent theme in both books is how development has not always made humans better-off or happier: Agriculture generated immiseration and disease in the short term, and there is no simple relationship between well-being and happiness. Science challenges religious dogma and traditional hierarchies organizing human life, but an alternative system of ethics placing humans at the center also lacks any objective or inherent justification. Advances in computing risk making humans themselves redundant and obsolete, as tasks can be better carried out by machines. Research on consciousness challenges our perceptions of what it means to be human, providing no foundation for traditional concepts such as 'the soul'. If humans at the core are nothing more than data-processing algorithms and biochemical processes, concepts such as individuality and free will are at best problematic and at worst meaningless. Moreover, differential access to technology can create new inequalities, with even more dramatic differences between the have and the have-nots. Harari is not an alarmist in a traditional sense, but forces us to ask new questions. In the world of the Old Testament, disasters stemmed from God's will, while we are now more likely to blame human disorganization such as the failures of WHO to stem the Ebola epidemic in West Africa. A reconsideration of what it means to be human may also increase our concerns for other species. Harari notes that numbers can be a deceptive measure of evolutionary success: Human interventions have led to large numbers of farm animals such as cows, but these are often treated abjectly by humans, without regard for their ability to suffer and emotional needs. Both volumes are insightful and an engaging, if occasionally unsettling read, and raise important questions for humankind as a species.