Aromatic polyethers are a group of high-performance engineering plastics which were developed by several chemical companies over the past forty years. Poly(phenylene ether)s mostly prepared by oxydative polycondensation of phenols, were the ﬁrst class of aromatic polyethers which was technically produced and commercialized [1-3]. Perfectly linear poly(arylene ether)s free of side chains can only be obtained by oxidative coupling of 2,6-disubstituted phenols. Therefore, the poly(2,6-dimethylphenylene-oxide), usually called PPO, is the most widely used poly(arylene ether). Its outstanding property is its compatibility with polystyrene (and a few other polymers) so that it is mainly used as component of blends . The oxidative coupling of phenols has intensively been studied between 1950 and 1980 (as discussed in the 1st edition of this handbook) but only few research activities were observed during the past 10 years discussed in the subchapter ‘Various Aromatic Polyethers’. Therefore the literature evaluated and discussed below mainly concerns poly(ether sulfone)s and poly(ether ketone)s. Furthermore, semiaromatic polyethers and aromatic polysulﬁdes are included in this chapter which mainly covers the literature of the years 1990 through spring 2000 (complementary to the ﬁrst edition).