The disclosure features novel lipids and compositions involving the same. Lipid nanoparticles include a novel lipid as well as additional lipids such as phospholipids, structural lipids, and PEG lipids. Lipid nanoparticles further including therapeutics and/or prophylactics such as RNA are useful in the delivery of therapeutics and/or prophylactics to mammalian cells or organs to, for example, regulate polypeptide, protein, or gene expression.
