The Acerbo Law was an Italian electoral law proposed by Baron Giacomo Acerbo and passed by the Italian Parliament in November 1923. The purpose of it was to give Mussolini's fascist party a majority of deputies.

In 1922, Italian Prime Minister Benito Mussolini became the leader of Fascist Italy as a result of the March on Rome. However he still only had 34 deputies in Parliament and 10 Nationalist allies. He was in a weak position and relied on a coalition with other parties that could easily unravel and force King Victor Emmanuel III to dismiss him. The idea was to change the voting system from proportional representation to a system which would allow Mussolini to have a clear majority.

The Acerbo Law stated that the party gaining the largest share of the votes – provided they had gained at least 25 percent of the votes – gained two-thirds of the seats in parliament. The remaining third was shared amongst the other parties proportionally.

Mussolini could only count on the support of 35 Fascist deputies and 10 Nationalists. The Law was passed on a majority vote. The obvious question is why a majority of deputies from other parties voted for the Law knowing that one way or another Mussolini would gain the 25% required. The Socialists voted against it but made no effort to coordinate other parties to oppose it. The PPI or Popolari were divided and leaderless after Mussolini had engineered the dismissal of Luigi Sturzo. The official policy was to abstain but 14 deputies voted for the measure. The smaller Liberal parties generally voted in favour. They lacked clear direction and many believed Mussolini's talk of strong government or hoped to keep their positions. There is no doubt that the presence of armed squadristi in the Chamber intimidated many into voting for the measure.

Benito Amilcare Andrea Mussolini (Italian pronunciation: [beˈniːto musːoˈliːni]; 29 July 1883 – 28 April 1945) was an Italian politician who led the National Fascist Party, ruling the country from 1922 to his ousting in 1943, and is credited with being one of the key figures in the creation of fascism.

Originally a member of the Italian Socialist Party and editor of the Avanti! from 1912 to 1914, Mussolini fought in World War I as an ardent nationalist and created the Fasci di Combattimento in 1919, catalyzing his nationalist and socialist beliefs in the Fascist Manifesto, published in 1921. Following the March on Rome in October 1922 he became the 27th Prime Minister of Italy and began using the title Il Duce by 1925, about which time he had established dictatorial authority by both legal and extraordinary means, aspiring to create a totalitarian state. After 1936, his official title was Sua Eccellenza Benito Mussolini, Capo del Governo, Duce del Fascismo e Fondatore dell'Impero ("His Excellency Benito Mussolini, Head of Government, Duce of Fascism, and Founder of the Empire") Mussolini also created and held the supreme military rank of First Marshal of the Empire along with King Victor Emmanuel III, which gave him and the King joint supreme control over the military of Italy. Mussolini remained in power until he was replaced in 1943; for a short period after this until his death, he was the leader of the Italian Social Republic.