Annum sacrum (English: 'Holy Year') is an encyclical by Pope Leo XIII on the consecration of the whole human race to the Sacred Heart of Jesus. It was delivered in St. Peter's Basilica on 25 May 1899, in the twenty-second year of his pontificate.

Annum sacrum was published on 25 May 1899, in anticipation of the Holy Year declared for 1900 to usher in the twentieth century.

When the Church, in the days immediately succeeding her institution, was oppressed beneath the yoke of the Caesars, a young Emperor saw in the heavens a cross, which became at once the happy omen and cause of the glorious victory that soon followed. And now, to-day, behold another blessed and heavenly tokenis offered to our sight-the most Sacred Heart of Jesus, with a cross rising from it and shining forth with dazzling splendor amidst flames of love. [...] there is in the Sacred Heart a symbol and a sensible image of the infinite love of Jesus Christ which moves us to love one another...

The consecration of the human race to the Sacred Heart of Jesus was a response to numerous demands that had been addressed to Pope Pius IX over 25 years. The encyclical, and the consecration, were influenced by two letters written to the pope by Sister Mary of the Divine Heart Droste zu Vischering who stated that in visions of Jesus Christ she had been told to request the consecration.

The motive of consecration is the need for the faithful to reciprocate God's love for His creation, especially for man.

The encyclical includes the Prayer of Consecration to the Sacred Heart of Jesus composed by Pope Leo XIII.

The Act of Consecration of the Human Race to the Sacred Heart of Jesus is a Roman Catholic prayer composed by Pope Leo XIII and included in the encyclical, published in Acta Apostolicae Sedis, as he consecrated the entire world to the Sacred Heart of Jesus.

As ordered by Pius XI, in the encyclical Quas primas (December 11, 1925) and published by the Sacred Congregation of Rites: