Deoxyribonucleic acid (DNA) hydrogel is a network of crosslinked DNA strands swollen in aqueous solutions. The crosslinks may be physical or chemical, such as the hydrogen bonds or ethylene glycol units, respectively, connecting the strands belonging to different double-helical DNA molecules. As DNA network strands in the hydrogels exhibit properties similar to those of the individual DNA molecules, such soft materials are a good candidate to make use of the characteristics of DNA such as coil-globule transition, biocompatibility, selective binding, and molecular recognition. Physical DNA hydrogels with an elastic modulus in the order of megapascals can be prepared by subjecting semidilute aqueous solutions of DNA to successive heating-cooling cycles between below and above the melting temperature of DNA. Chemical DNA hydrogels can be prepared by connecting the amino groups on the nucleotide bases through covalent bonds to form a three-dimensional DNA network in aqueous solutions. In this article, we summarize the preparation strategies of DNA hydrogels with a wide range of tunable properties. (c) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 551-556, 2011