Annum Sacrum is an encyclical

Encyclical

An encyclical was originally a circular letter sent to all the churches of a particular area in the ancient Catholic Church. At that time, the word could be used for a letter sent out by any bishop...

 by Pope Leo XIII

Pope Leo XIII

Pope Leo XIII , born Vincenzo Gioacchino Raffaele Luigi Pecci to an Italian comital family, was the 256th Pope of the Roman Catholic Church, reigning from 1878 to 1903...

 on the consecration of the entire world to the Sacred Heart of Jesus. It was delivered in Saint Peter's Basilica in Rome on the 25th day of May, 1899, the twenty-second year of his pontificate.

The consecration in the encyclical entered new theological territory by consecrating non-Christians. The encyclical, and the consecration, were influenced by two letters written to the pope by Sister Mary of the Divine Heart

Mary of the Divine Heart

Blessed Mary of the Divine Heart , born Maria Droste zu Vischering, was a German Roman Catholic nun best known for influencing Pope Leo XIII's consecration of the world to the Sacred Heart of Jesus...

 who stated that in visions of Jesus Christ

Visions of Jesus and Mary

Since the Crucifixion of Jesus Christ on Calvary until today, a number of people have claimed to have had visions of Christ and personal conversations with him. Some people make similar claims regarding the Blessed Virgin Mary. Discussions about the authenticity of these visions have often invited...

 she had been told to request the consecration.

The encyclical includes the Prayer of Consecration to the Sacred Heart

Prayer of Consecration to the Sacred Heart

The Prayer of Consecration to the Sacred Heart is a Roman Catholic prayer composed by Pope Leo XIII. It was included in the 1899 encyclical Annum Sacrum issued by Leo XIII as he consecrated the entire world to the Sacred Heart of Jesus....

 composed by Leo XIII.

See also

• Act of Consecration to the Sacred Heart of Jesus
  Act of Consecration to the Sacred Heart of Jesus
  The Act of Consecration to the Sacred Heart of Jesus is a Roman Catholic prayer by Saint Marguerite Marie Alacoque. It is was part of the private revelations reported by her regarding the Sacred Heart of Jesus.-Words of the prayer:...
  
  
• Alliance of the Hearts of Jesus and Mary
  Alliance of the Hearts of Jesus and Mary
  The Alliance of the Hearts of Jesus and Mary refers to the historical, theological and spiritual links in Catholic devotions to the Sacred Heart of Jesus and the Immaculate Heart of Mary...
  
  
• Consecration and entrustment to Mary
  Consecration and entrustment to Mary
  For centuries, Marian devotions among Roman Catholics have included many examples of personal or collective acts of consecration and entrustment to the Virgin Mary, with the Latin terms oblatio, servitus, commendatio and dedicatio having been used in this context.Consecration is an act by which a...
  
  
• Mary of the Divine Heart
  Mary of the Divine Heart
  Blessed Mary of the Divine Heart , born Maria Droste zu Vischering, was a German Roman Catholic nun best known for influencing Pope Leo XIII's consecration of the world to the Sacred Heart of Jesus...
  
  
• Sacred Heart of Jesus

Sources

• Vatican website: Annum Sacrum http://www.vatican.va/holy_father/leo_xiii/encyclicals/documents/hf_l-xiii_enc_25051899_annum-sacrum_en.html