"For whom the bell tolls" is a line from a poem by John Donne (pronounced like "Dunn") written in the early 1600s. Hemingway used a line from the poem as the title of a novel he wrote in the 20th century.
The poem goes like this (the copyright is in the public domain):
No man is an island, Entire of itself. Each is a piece of the continent, A part of the main. If a clod be washed away by the sea, Europe is the less. As well as if a promontory were. As well as if a manor of thine own Or of thine friend's were. Each man's death diminishes me, For I am involved in mankind. Therefore, send not to know For whom the bell tolls, It tolls for thee.
