Lyngdal (help·info) is a municipality in Vest-Agder county, Norway. Lyngdal was established as a municipality on 1 January 1838 (see formannskapsdistrikt). Austad and Kvås were separated from Lyngdal on 1 January 1909 but they were again merged with Lyngdal on 1 January 1964, together with the area of Spangereid west of Lenesfjorden.
It is a coastal municipality, and borders to the southeast Lindesnes municipality, Audnedal to the northeast, Hægebostad to the north, and Kvinesdal and Farsund to the west. Lyngdal declared township on 1 January 2001.
The Old Norse form of the name was Lygnudalr. The first element is the genitive case of the river name Lygna and the last element is dalr which means "valley" or "dale". The river name is derived from logn which means "quietness" and so the meaning is "the quiet one". Before 1908, the parish (but not the municipality) of Lyngdal was called Aa.