DNA strands are held together by hydrogen bonds between complementary base pairs on opposite strands. These base pairs are adenine (A) with thymine (T), and cytosine (C) with guanine (G). The hydrogen bonds between these base pairs are what give the DNA molecule its double-stranded structure. The backbone of the DNA molecule, which consists of alternating deoxyribose and phosphate groups, is held together by covalent bonds.