Vọng cổ (literally "longing for the past") is a Vietnamese song and musical structure used primarily in the cải lương theater music and nhạc tài tử chamber music of southern Vietnam. It was composed sometime between 1917 and 1919 by a Mr. Cao Văn Lầu (also called Sáu Lầu or Sáu Làu), of Bạc Liêu, a province in southern Vietnam (Trainor 1975). The song achieved great popularity and eventually its structure became the basis for numerous other songs. The tune is essentially melancholy in character and is sung using Vietnamese modal inflections.
Vọng cổ is a Sino-Vietnamese word for 望古.