Blazars are among the most intriguing and consistently bright objects in the observable Universe. They are the most extreme active galactic nuclei with powerful relativistic jets extending out to kpc from the central engine. Despite decades of systematic study of their emission across the electromagnetic spectrum, we still lack a basic understanding of their intrinsic jet processes and the processes relevant to the supermassive black holes that power them. Understanding how black holes interact with their environments, as well as the consequences of such interactions, has rippling effects not only across astrophysics, but also for fundamental physics and beyond. This is in fact the perfect time to study blazars and their jets. Advances in radio, optical, continued operations of Swift in X-rays and Fermi in γ-rays, IceCube in neutrinos, as well as the upcoming large-scale surveys set the ideal stage to study the multimessenger emission and structure of blazars on diverse scales. In addition, 2021 marked the beginning of the era of high-energy polarization with the launch of the Imaging X-ray Polarimetry Explorer. The symposium comes at the right time to recollect all that we know about blazars, all that we have yet to learn, and to organize the community and facilitate the building of new collaborations that will allow us, in this multimessenger era, to take advantage of the wealth of existing and upcoming facilities and tackle the major open questions in astrophysical jets.