Final answer:
The two strands of the DNA double helix are connected by hydrogen bonds between complementary base pairs, which plays a critical role in the stability and function of DNA.
Step-by-step explanation:
The two strands of the DNA double helix are held together by hydrogen bonds between base pairs. In DNA, the sugar-phosphate backbones of the two strands are connected by these hydrogen bonds. Specifically, adenine pairs with thymine via two hydrogen bonds, and cytosine pairs with guanine via three hydrogen bonds. These hydrogen bonds are essential for the stability of the DNA's double helix structure and allow the two strands to complement each other, making the DNA a reliable medium for genetic information.