The diffuse interstellar bands (DIBs) are absorption features that are seen toward reddened stars. They are caused by the absorption of light by the interstellar medium. Numbering hundreds of bands, the DIBs vary in strengths and in profiles and are detected in the near ultraviolet to the near infrared range. The bands are the signature of carriers that are ubiquitous in the interstellar medium making their identification an essential element for a correct understanding of the nature and the evolution of the interstellar medium. The diffuse bands have represented a long standing, fascinating challenge for astrophysics since they were first discovered more than a century ago. The search for the carriers of the DIB has motivated efforts at the frontiers of science, leading, among other things, to advances in spectroscopy and to the discovery of the fullerene molecules. Recent findings have shed light on the nature of the carriers of the DIBs and the role played by complex organic molecules in space. Recent progress in astronomical observations and in laboratory studies will be presented together with a discussion of the current consensus regarding this important issue.