"Lions led by donkeys" is a phrase popularly used to describe the British infantry of the First World War and to blame the generals who led them. The contention is that the brave soldiers (lions) were sent to their deaths by incompetent and indifferent leaders (donkeys). The phrase was the source of the title of one of the most scathing examinations of British First World War generals, The Donkeys—a study of Western Front offensives—by politician and writer of military histories Alan Clark. The book typified the mainstream First World War history of the 1960s, was vetted by Basil Liddell Hart and helped to form a popular view of the First World War (in the English-speaking world) in the decades that followed. The work's viewpoint of incompetent military leaders was never accepted by some mainstream historians like John Terraine and both the book and its viewpoint have been criticised.

The phrase has been applied more broadly to the leaders on both sides, implying that the War was a pointless waste of life, regardless of the technical competence or otherwise of generals on either side. Conversely, critics of the phrase have argued that, from the British viewpoint, the war was "necessary and successful".