Various pi-conjugated polymers are obtained by using organometallic polycondensation mediated by organotransition-metal complexes. For example, Ni(0) complex-mediated dehalogenation polycondensation of dihaloaromatic compounds XArX affords poly(arylene)s (Ar)(n),. These polymers show interesting electronic and optical properties and have already found several useful future applications such as battery, EL, diode, nonlinear optical device, etc. In this review, preparation, basic properties and practical applications for electronic and optical devices of pi-conjugated polymers will be described.