As a newly emerged protocol for the synthesis of conjugated polymers, direct arylation polymerization (DArP) is an environmentally friendly and cost-effective alternative to traditional methods of polymerization. DArP efficiently yields conjugated polymers with high yield and high molecular weight. However, DArP is also known to produce defects in polymer chemical structure. Together with molecular weight and polydispersity, these defects are considered to be important parameters of polymer structure and they have a strong impact on optical, electronic and thermal properties of conjugated polymers. The four major classes of conjugated polymer defects inherent for DArP have been identified: homocoupling regiodefects, branching defects, end group defects, and residual metal defects. To have a precise control over the polymer properties, it is important to understand what causes the defects to form during the polymerization process and be able to control their content. Here within the scope of current literature, we discuss in detail the definition and origin of all these defects, their influence on polymer properties and effective means to control the defects through fine tuning of the DArP reaction parameters. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 135-147