Chondrules are spherical silicate grains which formed from protoplanetary disk material, and as such provide an important record of the conditions of the Solar System in pre-planetary times. Chondrules are a major constituent in chondritic meteorites, however despite being recognised for over 200 years, their origins remain enigmatic. This comprehensive review describes state-of-the-art research into chondrules, bringing together leading cosmochemists...