Concluding talk-seminar on critical issues in development of new linear colliders

The growth of particle colliders is summarized, with their collision energy in the frame of the elementary constituents given for numerous specific machines. The logic concerning the design of electron-positron colliders and definition of parameters are briefly discussed. Several issues are covered which are presently uncertain, including beamstrahlung and interaction among beams of transverse dimensions in the angstrom range. Alternate power sources and their economy are considered as well as superconducting structures