While the origin of the diffuse interstellar bands in interstellar rather than stellar material was established soon after their discovery early in the 20th century, their precise identification has eluded generations of astronomers. However, advances in optical techniques, laboratory studies of astrophysically relevant materials, and our general understanding of the interstellar medium may be changing that. Current indications are that the carrier is molecular in origin. The 40 invited reviews in this text aim to bring the reader to the forefront of research, covering observation, theory and laboratory experiments.