Lucy Wills, MA (Cantab), LRCP, MB BS (Lond) (10 May 1888 – 26 April 1964) was a leading English haematologist. She conducted seminal work in India in the late 1920s and early 1930s on macrocytic anaemia of pregnancy. Her observations led to her discovery of a nutritional factor in yeast which both prevents and cures this disorder. Macrocytic anaemia is characterised by enlarged red blood cells and is life-threatening. Poor pregnant women in the tropics with inadequate diets are particularly susceptible. The nutritional factor identified by Lucy Wills (the ‘Wills Factor’) was subsequently shown to be folate, the naturally occurring form of folic acid.