The site selection for the future large European telescope is a key issue, which will be addressed within the Euorpean proposal to be submitted to be funded by the EECC within the ELT design studies proposal. The organization, working scheme and baseline frameworks have been discussed and planned and are summarized here. For the definition of the working package (the WP 12000 of the proposal) important use have been done of all efforts been carried out during the last decade in the definition of techniques and tools reliable for the study of the atmosphere over observing sites. Also important is the relevance that the studies of the atmosphere have acquired, becoming key projects for most important astronomical sites. Therefore we have also taken advantage of the number of data already available which have naturally defined a ranking among the known places, which have also been taken as a base line for pre-selecting the candidate sites.