Thanks to the recent observation of a high-energy neutrino by IceCube, coincident with a remarkable flaring episode identified by Fermi LAT, the blazar TXS 0506+056 is now famous as the first confirmed source of high-energy neutrinos and extragalactic cosmic rays. I will present data from a multiwavelength observing campaign, initiated within seconds of the neutrino detection, which characterize TXS 0506+056 in detail, from near-infrared to gamma-rays, for over a month following its neutrino detection. In an extensive modeling effort, we have used these data to explore the blazar’s physical conditions for high-energy neutrino production. I will also address the importance of regular monitoring of blazars across the electromagnetic spectrum with different telescopes (such as Fermi and Swift) in order to clarify the nature of their acceleration processes. In the next few years, Fermi gamma-ray data will play a crucial role in conducting sensitive searches for multimessenger sources.