The major role of antioxidant tea catechins (polyphenols) is being increasingly recognized with regard to human health and cancer prevention. In this book, we review the effects of tea catechins on DNA and RNA structures and dynamics. The conjugation and binding efficacy of tea catechins (+)-catechin (C), (¿)-epicatechin gallate (ECG) and (¿)-epigallocatechin gallate (EGCG) with calf thymus DNA and transfer RNA were analysed. Thermodynamic analysis showed that tea catechins bind DNA and tRNA via hydrophilic and hydrophobic interactions with the binding efficacy of 40-60%. Larger catechins form more stable DNA and tRNA adducts with the order of stability EGCG>ECG>C. Modeling showed that catechin-polynucleotide bindings occur via both G-C, A-T and A-U base pairs with the free binding energies of -4.4 to -4.6 (C), -4.5 to -4.7 (EGC) and -4.6 to -4.7 kcal/mol (EGCG). Tea polyphenols binding induced major alterations of DNA and tRNA structures, while biopolymers remain in native conformations.