Sum: Forty Tales from the Afterlives, also simply called Sum, is a work of speculative fiction by American neuroscientist David Eagleman. It is in press in 28 languages as of 2016. The Los Angeles Times described it as "teeming, writhing with imagination." Barnes and Noble named it one of the Best Books of 2009.

David Eagleman is an American neuroscientist, author, and science communicator. He teaches neuroscience at Stanford University and is CEO and co-founder of Neosensory, a company that develops devices for sensory substitution. He also directs the non-profit Center for Science and Law, which seeks to align the legal system with modern neuroscience and is Chief Science Officer and co-founder of BrainCheck, a digital cognitive health platform used in medical practices and health systems. He is known for his work on brain plasticity, time perception, synesthesia, and neurolaw.