ALDH1A1 (Aldehyde Dehydrogenase 1 Family Member A1) is an enzyme that plays a crucial role in the metabolism of retinoids and detoxification of aldehydes. It is part of the aldehyde dehydrogenase (ALDH) family, which is involved in the conversion of toxic aldehydes into non-toxic carboxylic acids. ALDH1A1 is most notably involved in the oxidation of retinaldehyde to retinoic acid, an important step in the synthesis of retinoic acid, a key molecule in regulating gene expression, cell differentiation, and embryonic development. ALDH1A1 is also implicated in stem cell biology, as it is used as a marker for stem cells and cancer stem cells in various tissues, including breast, colon, and liver cancer. Additionally, ALDH1A1 plays a role in cellular protection by metabolizing reactive aldehydes generated under oxidative stress conditions. Its dysregulation is associated with cancer progression, drug resistance, and neurological disorders.