The 4th Aris Lecture in Tibetan and Himalayan Studies was delivered by Dr Sam van Schaik (British Library) on 15th November 2018 at Wolfson College, Oxford. The lecture was introduced by Professor Ulrike Roesler. Books of spells are a constant but little studied aspect of Tibetan Buddhism. Used by lay people as well as monks and nuns, they contain a variety of rituals covering divination, healing and protection, making rain and stopping hail, and summoning and exorcising spirits and demons. Some books of spells contain other kinds of spells as well, such as to make someone fall in love, or to gain powers of clairvoyance, invisibility, and finding hidden treasure. Some, but not all books of spells contain aggressive spells -- what we commonly call 'black magic'. This talk looks at the role of books of spells in Tibetan Buddhism, and how the use of magic fits within the Buddhist ethical framework.