Since plant derived bioactive compounds have been attributed a variety of health-promoting effects, the extraction of these compounds from plant material has become an important industrial process. Nowadays, green extraction process such as subcritical water extraction, which provides higher selectivities, low cost and shorter extraction times, is very popular. Pressurized liquid extractor (PLE, Dionex trade name accelerated solvent extractor-ASE) technology has also been used for subcritical water extraction of bioactive compounds from various plant materials as well as laboratory-built apparatus. Flaxseed is the richest source of secoisolariciresinol diglucoside (SDG) lignan and also other phenolics which have phytoestrogenic, anticarcinogenic, antioxidative and cardioprotective effects. This book, therefore, includes extraction of phenolic compounds from flaxseed (Linum usitatissimum L.) meal sticks with subcritical water using ASE. Also, useful informations about ASE and validation study of SDG lignan analysis in HPLC-MS/MS are illustrated in this book.