HAWC the Mexico-US Collaboration to build the highest energy gamma ray observatory

In 2008 groups from 14 institutions in the US and 11 from Mexico got together creating the HAWC Collaboration with the aim to build a frontier observatory in the mountains of central Mexico at 4,100 MASL to detect the highest energy gamma rays from galactic and extragalactic sources. After some years of R&D, prototyping of arrays of detectors and defining the final configuration of the observatory, proposals were approved. Funding was obtained from the NSF channeled through the University of Maryland, DoE through Los Alamos National Laboratory and Conacyt based in the Physics Institute of the National University of Mexico, UNAM. The way the collaboration was organized, the experiences and lessons learnt in a project involving two countries and three funding agencies and 25 institutions will be presented. The HAWC gamma ray observatory was successfully built in time and within budget by 2014 and has been in continuous operation since, providing a wealth of insight on the most violent regions of the Universe.