[en] The multi-group, multi-temperature libraries ECCOLIB-JEFF-3.1, derived from the JEFF-3.1 evaluations, have been produced using the NJOY-99 and CALENDF-2005 processing codes and the MERGE-3.8 and GECCO-1.4 interface tools. The processing steps are explained along side the Quality Assurance processes linked to such libraries. Final results encompass five main libraries; two fine 1968 group with probability tables for 104 major isotopes allowing detailed criticality studies, another in the same groups structure for the thermal compounds, and two others in coarser 172 XMAS and 175 Vitamin-J group structures for other criticality and shielding, transport studies. (authors)