Dodecanoylcarnitine is an acylcarnitine. More specifically, it is an dodecanoic acid ester of carnitine. Acylcarnitines were first discovered more than 70 year ago (PMID: 13825279). It is believed that there are more than 1000 types of acylcarnitines in the human body. The general role of acylcarnitines is to transport acyl-groups (organic acids and fatty acids) from the cytoplasm into the mitochondria so that they can be broken down to produce energy.  This process is known as beta-oxidation. According to a recent review [Dambrova et al. 2021, Physiological Reviews], acylcarnitines (ACs) can be classified into 9 different categories depending on the type and size of their acyl-group: 1) short-chain ACs; 2) medium-chain ACs; 3) long-chain ACs; 4) very long-chain ACs; 5) hydroxy ACs; 6) branched chain ACs; 7) unsaturated ACs; 8) dicarboxylic ACs and 9) miscellaneous ACs. Short-chain ACs have acyl-groups with two to five carbons (C2-C5), medium-chain ACs have acyl-groups with six to thirteen carbons (C6-C13), long-chain ACs have acyl-groups with fourteen to twenty once carbons (C14-C21) and very long-chain ACs have acyl groups with more than 22 carbons. Dodecanoylcarnitine is therefore classified as a medium chain AC. As a medium-chain acylcarnitine Dodecanoylcarnitine is somewhat less abundant than short-chain acylcarnitines. These are formed either through esterification with L-carnitine or through the peroxisomal metabolism of longer chain acylcarnitines (PMID: 30540494). Many medium-chain acylcarnitines can serve as useful markers for inherited disorders of fatty acid metabolism. In particular Dodecanoylcarnitine is elevated in the blood or plasma of individuals with very long chain acyl-CoA dehydrogenase deficiency (PMID: 9034211), Yin deficiency (PMID: 31909891), multiple acyl coenzyme A dehydrogenase deficiency (PMID: 30510944), CVD in type 2 diabetes Mellitus (PMID: 32431666), and diastolic heart failure (PMID: 26010610). It is also decreased in the blood or plasma of individuals with Celiac disease (PMID: 16425363), psoriasis (PMID: 28695330), intracerebral hemorrhage (PMID: 29265114), and pregnancy (PMID: 24704061 - in serum of pregnant women with fetus with CHD). Dodecanoylcarnitine is elevated in the urine of individuals with renal cell carcinoma (PMID: 29658093). Carnitine octanoyltransferase (CrOT, EC:2.3.1.137) is responsible for the synthesis of all medium-chain (MCAC, C5-C12) and medium-length branched-chain acylcarnitines in peroxisomes (PMID: 10486279). Dodecanoylcarnitine is also present in fatty acid oxidation disorders such as long-chain acyl CoA dehydrogenase deficiency, carnitine palmitoyltransferase I deficiency, and carnitine palmitoyltransferase II deficiency (PMID: 12828998 ). The study of acylcarnitines is an active area of research and it is likely that many novel acylcarnitines will be discovered in the coming years. It is also likely that many novel roles in health and disease will be uncovered. An excellent review of the current state of knowledge for acylcarnitines is available at [Dambrova et al. 2021, Physiological Reviews].