Blue lettuce can refer to:
Cicerbita alpina (synonym Lactuca alpina), tall blue lettuce or alpine sow-thistle, native to upland and mountainous parts of Europe
Lactuca biennis, tall blue lettuce or blue wood lettuce, native to the eastern half of the United States and Canada
Lactuca canadensis, Florida blue lettuce or Canada blue lettuce, considered to be a native to parts of North America and introduced elsewhere
Lactuca perennis, blue lettuce, native to Central and Southern Europe
Lactuca tatarica, blue lettuce, widespread species found in Europe, Asia and North America
