From the Vatican: 

Pope Francis will consecrate Russia and Ukraine to the Immaculate Heart of Mary on Friday, 25 March, during the Celebration of Penance that he will preside over at 5pm in St Peter’s Basilica.

The Director of the Holy See Press Office, Matteo Bruni, said in a statement: “The same act, on the same day, will be performed in Fatima by Cardinal Konrad Krajewski, papal almoner,” who is being sent there by the Pope.

The day of the Feast of the Annunciation of the Lord was chosen for the consecration.

In the apparition of 13 July 1917, in Fatima, Our Lady had asked for the consecration of Russia to Her Immaculate Heart, stating that if this request were not granted, Russia would spread “its errors throughout the world, promoting wars and persecution of the Church.”

“The good,” she added, “will be martyred; the Holy Father will have much to suffer, various nations will be destroyed.”

“The same act, on the same day, will be performed in Fatima by Cardinal Konrad Krajewski, papal almoner.”

After the Fatima apparitions there were various acts of consecration to the Immaculate Heart of Mary.

Pope Pius XII, on 31 October 1942, consecrated the whole world, and on 7 July 1952 he consecrated the peoples of Russia to the Immaculate Heart of Mary in the Apostolic Letter Sacro vergente anno:

“Just as a few years ago we consecrated the whole world to the Immaculate Heart of the Virgin Mother of God, so now, in a most special way, we consecrate all the peoples of Russia to the same Immaculate Heart.”

On 21 November 1964, Pope St Paul VI renewed the consecration of Russia to the Immaculate Heart in the presence of the Fathers of the Second Vatican Council.

Pope St. John Paul II composed a prayer for what he called an ‘Act of Entrustment’ to be celebrated in the Basilica of St Mary Major on 7 June 1981, the Solemnity of Pentecost.

Read more. 

It’s worth noting that there’s been some dispute about whether the original consecration to Russia took place as Mary had desired:

There have been a number of consecrations of both Russia and the world to the Immaculate Heart of Mary, made by different popes (including several by Pope Pius XII and St. John Paul II, and one by Pope Francis on Oct. 13, 2013). But according to Sr. Lucia of Fatima, the 1984 consecration by St. John Paul II satisfied the request Heaven made in 1929 for the consecration of Russia to the Immaculate Heart.

In the Congregation of the Doctrine of the Faith’s “The Message of Fatima,” released June 26, 2000, as part of the Holy See’s official publication and interpretation of the secret of Fatima, we read (emphasis added):

Sister Lucia personally confirmed that this solemn and universal act of consecration corresponded to what Our Lady wished (“Sim, està feita, tal como Nossa Senhora a pediu, desde o dia 25 de Março de 1984”: “Yes it has been done just as Our Lady asked, on 25 March 1984”: Letter of 8 November 1989). Hence any further discussion or request is without basis.

In Fatima for Today by world-renowned expert on Fatima Fr. Andrew Apostoli, CFR (Ignatius Press, 2010), pages 193-199 and in Appendix C, he lays out evidence that St. John Paul II understood the consecration requested by Our Lady to have taken place, in large part because Sr. Lucia confirmed it repeatedly in letters and to Fr. Luis Kondor, the vice-postulator for the causes of Sts. Jacinta and Francisco.

Father Michael Gaitley, MIC, follows this line in his The Second Greatest Story Ever Told (Marian Press, 2015), Chapter 8. Here’s his discussion of whether or not the 1984 consecration counted:

On March 25, 1984, in St. Peter’s Square, with a crowd of about 200,000 of the faithful, with numerous bishops and cardinals present, in union with all the bishops throughout the world, and before the Fatima Shrine statue of Our Lady, Pope John Paul II solemnly consecrated the world and Russia to Mary’s Immaculate Heart as had been requested by Our Lady of Fatima. However, unfortunately, because the Pope did not explicitly say “Russia” in his public prayer, choosing instead to use veiled references as Pius XII had done, some have argued that it did not count.

But it did count because the Pope clearly implied Russia when he said, “In a special way we entrust and consecrate to you those individuals and nations that particularly need to be thus entrusted and consecrated.” He clearly intended to consecrate Russia, as did the bishops, who undoubtedly understood the implication.

After the ceremony, when he was thanked for consecrating “the world,” John Paul himself added, “and Russia.” This point of including Russia was deeply meaningful to him, because his own home country, Poland, was still suffering behind the Iron Curtain. In fact, many have speculated that during the several pauses John Paul made while reciting the World Consecration and the Triumph consecration prayer, he was probably bringing this intention of his heart even more directly to Our Lady, namely, his prayer for the collapse of Soviet Communism.

Meanwhile, The Pillar offers this explainer:

Personal consecrations can be renewed as an act of faith and devotion, and often are. And in early March, the Latin Catholic bishops of Ukraine asked Pope Francis to “publicly perform the act of consecration to the Sacred Immaculate Heart of Mary of Ukraine and Russia, as requested by the Blessed Virgin in Fatima.”

The new consecration is not a concession from the Holy See that the 1984 consecration was in some way insufficient, but this act will be more explicit, presumably naming Russia and Ukraine in the prayers themselves. That may well spark new rounds of conspiracy theories about past consecrations, or be taken as a sign that Pope St. John Paul II did not really complete the consecration.

But more likely, Pope Francis intends his prayers to be acts of renewal — pleas to God, and the Blessed Virgin Mary — in a time of great hardship, rather than making up for previous acts called into question.