[[Image:The moon high above Cerro Chajnantor at sunset.jpg|thumb|The [[moon]] high above Cerro Chajnantor at [[sunset]].]]
ALMA ishas aits fusion of ideas, with itsconceptual roots in three astronomical projects: the Millimeter Array (MMA) of the United States, the Large Southern Array (LSA) of Europe, and the Large Millimeter Array (LMA) of Japan.
The majorfirst breakthroughstep occurredtoward the creation of what would become ALMA came in 1997, when [[European Southern Observatory|ESO]] (European Southern Observatory) and [[National Radio Astronomy Observatory|NRAO]] (National Radio Astronomy Observatory) agreed to pursue a common project that merged the MMA and LSA into what would eventually be named ALMA. The merged array combined the sensitivity of the LSA with the frequency coverage and superior site of the MMA. ESO and NRAO worked together in technical, science, and management groups to define and organize a joint project between the two observatories with participation by Canada and Spain (which didn't belong to ESO at that time).
A flurryseries of resolutions and agreements ensued, including the choice of "Atacama Large Millimeter Array", or ALMA, for as the name of the new array in March 1999. This effort culminated in the signing of the ALMA Agreement on February 25, 2003, between the North American and European parties. Following mutual discussions over several years, the ALMA Project received a proposal from [[National Astronomical Observatory of Japan|NAOJ]] (National Astronomical Observatory of Japan) whereby Japan would provide the ACA (Atacama Compact Array) and three additional receiver bands for the large array, to form Enhanced ALMA. Further discussions between ALMA and NAOJ led to the signing of a high-level agreement on September 14, 2004, that makes Japan an official participant in Enhanced ALMA, to be known as the Atacama Large Millimeter/submillimeter Array.
During an early stage of the planning of ALMA, it was decided to employ ALMA antennas designed and constructed fromby renownknown companies in North America, Europe and Japan rather than using one single design. This was mainly for political reasons. Although very different approaches have been chosen by the providers, each of the antenna designs appears to be able to meet ALMA's stringent requirements.
