The High Altitude Water Cherenkov Experiment or High Altitude Water Cherenkov Observatory (also known as HAWC) is a gamma-ray and cosmic ray observatory located on the flanks of the Sierra Negra volcano in the Mexican state of Puebla at an altitude of 4100 meters, at . HAWC is the successor to the Milagro gamma-ray observatory in New Mexico, which was also a gamma-ray observatory based around the principle of detecting gamma-rays indirectly using the water Cherenkov method. HAWC is a joint collaboration between a large number of American and Mexican universities and scientific institutions, including the University of Maryland, the National Autonomous University of Mexico, the National Institute of Astrophysics, Optics and Electronics, Los Alamos National Laboratory, NASA/Goddard Space Flight Center, the University of California, Santa Cruz, Michigan Technological University, Michigan State University, Benemérita Universidad Autónoma de Puebla, the Universidad de Guadalajara, the University of Utah, the University of New Mexico, the University of Wisconsin–Madison and the Georgia Institute of Technology. Overview The HAWC Gamma-ray Observatory is a wide field of view, continuously operating, TeV gamma-ray telescope that explores the origin of cosmic rays, study the acceleration of particles in extreme physical environments, and search for new TeV physics. HAWC was built at an elevation of 4100 m above sea level in Mexico by a collaboration of 15 US and 12 Mexican institutions, and it is operated with funding from the US National Science Foundation, the US Department of Energy and CONACyT (Mexico's science funding agency). HAWC was completed in spring of 2015, and consists of an array of 300 water Cherenkov detectors. It is designed to be more than an order of magnitude more sensitive than its predecessor, Milagro. HAWC monitors the northern sky and makes coincident observations with other wide field of view observatories. HAWC work with other observatories, such as VERITAS, HESS, MAGIC, IceCube and later, CTA, so they can make overlapping multi-wavelength and multi-messenger observations and to maximize coincident observations with the Fermi Gamma-ray Space Telescope (Fermi). HAWC has the ability to detect a large ensemble of gamma-ray sources, measuring their spectra and variability to characterize TeV scale acceleration mechanisms. In a one-year survey, HAWC can perform a deep, unbiased survey of the TeV gamma-ray with a 50 mCrab sensitivity at 5σ. HAWC will observe hard-spectrum (high photon energies) Galactic sources in the TeV with a sensitivity similar to that of Fermi in the GeV, detect