The European Southern Observatory is developing a concept of ground-based, 100-m class optical telescope, with segmented primary and secondary mirrors, integrated active optics and multi-conjugate adaptive optics capabilities. Preliminary analysis have confirmed feasibility of the major telescope components within a cost on the order of 1,000 million Euros and within a competitive time frame. The modular design allows progressive transition between integration and science operation, and the telescope would be able to deliver full resolution and unequalled collecting power 11 to 12 years after project funding. The concept owes much of its design characteristics to features of existing telescopes, namely the Hobby-Eberly for optical fabrication, the Keck for optical segmentation, and the VLT for active optics control. The only critical area in terms of needed development seems to be multi-conjugate adaptive optics, but its principles have recently been confirmed experimentally and rapid progress in the underlying technologies is taking place and benefits from consumer applications. Further studies are progressing, confirming initial estimates, and a baseline design is taking shape. The primary objective of those studies is to demonstrate feasibility within proven technologies, but provisions are made for likely technological progress allowing either cost reduction or performance improvement, or both.