In　the　past　several　decades,　heat　transfer　enhancements　using　extended　surface　(fins)　has　received　considerable　attention.　A　new　heat　transfer　enhancement　technique,　longitudinal　vortex　generators　(LVGs),　has　received　significant　attention　since　the　1990s.　It　is　activated　by　a　special　type　of　extended　surface　that　can　generate　vortices　with　axes　parallel　to　the　main　flow　direction.　The　vortices　result　from　strong　swirling　secondary　flow　caused　by　flow　separation　and　friction.　The　state-of-the-art　on　research　and　applications　of　LVG　are　described　here.　The　topical　coverage　includes　heat　transfer　enhancement　in　straight　channels　and　in　heat　exchangers.　Among　the　latter　are　plate　and　wavy　fin-and-tube　heat　exchangers,　fin-and-oval-tube　heat　exchangers,　and　fin-and-tube　heat　exchangers　with　multiple　rows　of　tubes.　The　trends　and　future　directions　of　heat　transfer　enhancement　by　means　of　LVG　are　discussed.　©　2012　Elsevier　Inc.