The methods and flow charts used for the industrial preparation of PET are shown and briefly discussed. Then, the three classes of contaminants usually appearing in PET are described and their causes elucidated. The organic contaminants impart to the produced PET an undesired yellow-amber tinge while those containing metal ions or elemental metals impart to the polymer various undesirable colors. Other organic contaminants are crosslinked gels and flakes, and especially the latter may cause filament rupture and may lead to the disruption of melt spin-draw processes. Some remedies to eliminate or minimize the appearance of such contaminants are then suggested, followed by a brief discussion of non-antimony catalysts which eliminate the gray discoloration usually imparted to PET by antimony-containing catalysts.