The type of bond that holds together the base pairs in DNA is the hydrogen bond. These are relatively weak bonds formed between specific nitrogenous bases of the two DNA strands: adenine pairs with thymine through two hydrogen bonds, and cytosine pairs with guanine through three hydrogen bonds. This complementary base pairing via hydrogen bonds is essential for the stable yet flexible double helix structure of DNA. The hydrogen bonds allow the two DNA strands to separate and rejoin easily during processes like replication and transcription, while the stronger covalent phosphodiester bonds maintain the sugar-phosphate backbone of each strand.