Molecular Biology: a field of science concerned with the way in which the molecules of life (DNA, RNA, and proteins for the most part) interact, regulate each other, and are modified within a cell. Not merely a subject but also a toolkit of techniques to gather information about biomolecules: the polymerase chain reaction (PCR), blotting, gel electrophoresis, microarrays to test for differences in gene expression on a large scale, DNA extraction methodologies, in situ hybridization techniques, and many, many more.

There is considerable overlap between molecular biology and biochemistry–the study of the structures and interactions between nucleic acids, proteins, sugars, and fat molecules–and between molecular biology and molecular genetics–which concerns itself with the genes, the outcome of their normal expression, and how the disruption of their expression can lead to disease.