The future planning working group of the optical and infrared astronomy community of Japan completed its two-year study to yield a concrete plan for ground based telescopes and space missions for the coming decades. The R&D issues towards the realization of extremely large telescopes reported in this paper include a novel optical design, development of new ceramic mirrors, high precision grinding approach to reduce the involved cost and time for fabricating aspheric segmented mirrors, and conceptual studies of instruments.

The present paper is essentially a slightly updated version of the paper presented in the workshop “Instrumentation for Extremely Large Telescopes” held at Ringberg Castle, Bavaria, 25-29 July 2005.