World's Day of Remembrance for Victims of Katyn Massacre is observed annually on April 13, primarily in Poland, but also recognized worldwide. This day commemorates the Katyn massacre, where approximately 22,000 Polish internees and military officers were executed by the NKVD in the spring of 1940, under the direction of Lavrentiy Beria. The massacre's discovery was publicly announced by German forces on April 13, 1945, leading to the Soviet Union's eventual admission of responsibility on the 47th anniversary of the event. On this day, solemn ceremonies are held at Katyn memorials globally, with Poland marking it as a national holiday, although it typically remains a working day unless it falls on a weekend. The observance serves to honor the victims and acknowledge the historical significance of the tragedy.