Anabolism collectively refers to all the processes of chemical reactions that build larger molecules out of smaller molecules or atoms; these processes are also known as anabolic processes or anabolic pathways. The opposite of anabolism is catabolism, the set of processes that breaks down larger molecules into smaller ones.

Anabolism, also called biosynthesis, the sequences of enzyme -catalyzed reactions by which relatively complex molecules are formed in living cells from nutrients with relatively simple structures.

Anabolism or biosynthesis is the set of biochemical reactions that construct molecules from smaller components. Anabolic reactions are endergonic, meaning they require an input of energy to progress and are not spontaneous. Typically, anabolic and catabolic reactions are coupled, with catabolism providing the activation energy for anabolism.