The interaction of complementary nucleic acid strands. Since DNA is a double-stranded structure held together by complementary interactions (in which C always binds to G, and A to T), complementary strands favorably reanneal or “hybridize” to each other when separated. This can occur between two DNA strands and also between DNA and RNA strands provided there is sufficient complementarity in their base sequence. Hybridization occurs in all physiological DNA reactions including replication, and transcription, and forms the basis of many molecular biology techniques including Southern and Northern blotting, PCR and sequencing.