Yekatit 12 (Amharic: የካቲት ፲፪, romanized: Yekatīt 12), also known in Italy as the Addis Ababa massacre (Italian: Strage di Addis Ababa), is a date in the Ge'ez calendar which refers to the massacre and imprisonment of Ethiopians by the Italian occupation forces following an attempted assassination of Marshal Rodolfo Graziani, Viceroy of Italian East Africa, on 19 February 1937. Graziani had led the Italian forces to victory over the Ethiopians in the Second Italo-Ethiopian War and was supreme governor of Italian East Africa. It has been described as the worst massacre in Ethiopian history.

Estimates vary on the number of people killed in the three days that followed the attempt on Graziani's life. Ethiopian sources claimed the Italians killed 30,000 people, while other estimates typically range between 1,400 and 6,000 deaths; a 2017 study of the massacre stated that approximately 19,200 people were killed, 20 percent of the population of Addis Ababa. Over the following week, numerous Ethiopians suspected of opposing Italian rule were rounded up and executed, including members of the Black Lions and other members of the aristocracy. Emperor Haile Selassie had sent 125 men abroad to receive college education, but most of them were killed. Many more were imprisoned, even collaborators such as Ras Gebre Haywot, the son of Ras Mikael of Wollo, Brehane Markos, and Ayale Gebre, who had helped the Italians identify the two men who made an attempt on Graziani's life.

Following the massacre, Graziani was deposed by Benito Mussolini and replaced by Prince Amedeo, Duke of Aosta.

Following the defeat of the Ethiopian forces under his personal command at the Battle of Maychew on 31 March 1936, Emperor Haile Selassie left Ethiopia to address the League of Nations to plead for their assistance against the Italians. He made his close friend and cousin Ras Imru Haile Selassie his regent during his absence, who attempted to set up a Provisional Government at Gore, in the southwestern part of the country. Gore, however, was located deep in the homeland of the Oromo people, who opposed his attempts to maintain imperial hegemony; some went as far as to approach the British to recognize their attempts to create a Western Galla Confederation. When the Italians advanced on Nekemte on 24 October, Ras Imru found his position untenable and marched south in search of more welcoming surroundings. The two opponents maneuvered over southwestern Ethiopia, the Italians pursuing the Ethiopians, through the month of November until Ras Imru was caught on the banks of the Gojeb River, where after fierce fighting Ras Imru surrendered on 18 December.

Meanwhile, loyalists made a poorly organized attempt to recapture Addis Ababa on 28 July 1936. Various armed groups of Ethiopians attacked the Italian positions in the capital city, taking the defenders by complete surprise; the first Italians they encountered were reportedly a group working on a well. However, General Gariboldi had expected an attack on the capital, and had prepared for this eventuality. Although a unit under Abebe Aragai had almost entered the Little Gebbi, where Graziani was working, the Ethiopians were repulsed on all sides. Despite a last rally by Abune Petros on the final day of the battle, who led a final advance in St George's Square, the attempt on the city failed.

Lastly, the remaining Ethiopian forces in the southeast were being run down. Ras Desta Damtew and Dejazmach Beyene Merid had remained in control of their provincial capitals at Irgalem and Goba through November. On 23 November a motorized column under Captain Tucci had penetrated into the region, sparking a revolt by the local Sidama people; Irgalem fell to the Italians on 1 December, and Ras Desta and Dejazmach Beyene Merid fell back into the mountains of Bale Province. A game of cat-and-mouse followed, until the last few thousand soldiers under their command were cornered near Lake Shala and annihilated by superior Italian numbers at the Battle of Gogetti 18 February 1937. Ras Desta managed to escape the battlefield alone, but was hunted down and executed a few days later. With Ras Desta Damtew's death, all organized Ethiopian resistance to the Italians was spent.

Despite having unquestioned control over the new Italian East Africa at the beginning of February 1937, Graziani still mistrusted its inhabitants. During the previous year, following the capture of Jijiga by his men, he was inspecting an Ethiopian Orthodox church when he fell through a concealed hole in the floor, which he was convinced had been prepared as a mantrap for him. "From that incident," writes Anthony Mockler, "it is possible to date his paranoiac hatred of and suspicion towards the Coptic clergy." Despite this, to celebrate the birth of the Prince of Naples, Graziani announced he would personally distribute alms to the poor on Friday, 19 February, at the Genete Leul Palace (also known as the Little Gebbi).

In the crowd that formed that Friday morning were two young Eritreans living in Ethiopia named Abraha Deboch and Mogus Asgedom. Finding their fortunes limited in the Italian colony, they had come to Ethiopia to enroll in the Menelik II School, where recent events had overtaken them. Apparently accommodating himself to the new administration, Abraha gained employment with the Fascist Political Bureau, where his Eritrean origin, knowledge of Italian, and familiarity with the city made him useful. However, according to Richard Pankhurst, Abraha Deboch was bitterly opposed to the Italians, especially its racist practices. Before leaving their house, Abraha had placed an Italian flag on the wooden floor, driven a bayonet through it, then tied an Ethiopian flag to the bayonet.