A Google-Geek like me can't stand to leave bald statements like that unanswered. So here they are:
These are the nine major approved Marian apparitions of modern times, based on their acceptance by the Church and the importance they have assumed over time. (See, for example, the article "Apparitions" in Fr. Michael Carroll's Theotokos, A Theological Encyclopedia of the Blessed Virgin Mary, p.47). Theotokos.org.uk
Mary appeared four times to Juan Diego in 1531 at Tepeyac hill near Mexico City. She proclaimed herself the spiritual mother of all mankind and left her miraculous image on Juan Diego's outer garment, his tilma. To this day Mexicans have a great devotion to Our Lady of Guadalupe.
Mary appeared to Catherine Labouré, in the chapel of the Daughters of Charity of St. Vincent de Paul, at Rue du Bac in Paris, three times in 1830. She showed her the design of the the medal of the Immaculate Conception, the "Miraculous Medal." This medal, when propagated, helped to renew devotion to Our Lady, both in France and eventually around the world.
Mary appeared to two children, Maximin Giraud, aged 11, and Mélanie Calvat, aged 14, in 1846, one afternoon while they were looking after the animals high up on the mountain. She appealed for penance and an end to Sabbath breaking and blasphemy in the region. This apparition is credited with a major revival of Catholicism in the area.
Mary appeared to Bernadette Soubirous, aged 14, a total of eighteen times at Lourdes in southern France, at the Grotto of Massabielle. She asked for penance and prayer for the conversion of sinners, and described herself as the "the Immaculate Conception." Lourdes is most famous for the miraculous spring which has been responsible for many cures accepted by the Church.
Mary appeared in the sky over the small town of Pontmain in north-western France to a group of young children for about three hours in January 1871, as the Franco-Prussian war was threatening the area. Her message appeared on a banner under her feet, and encouraged prayer while emphasising Jesus' love and concern. The village was spared invasion.
Mary appeared at Knock, a small village in Count Mayo, Ireland in August 1879. A number of villagers of diverse ages saw a silent apparition, which lasted about three hours, outside the gable end of the local church. They saw three figures, Mary, Joseph, and St John the Apostle, as well as a lamb on an altar and angels.
Three children, Lucia de Santos, aged 10, and her two cousins, Francisco Marto, aged 9, and Jacinta Marto, aged 7, saw Mary six times between May and October 1917. She described herself as "Our Lady of the Rosary," while urging prayer, and particularly the rosary, as well as penance for the conversion of sinners, and the consecration of Russia to her Immaculate Heart.
Mary appeared thirty-three times to a group of children in the winter of 1932-33 at Beauraing in Belgium, in a convent garden near a hawthorn tree. She described herself as "the Immaculate Virgin" and "Mother of God, Queen of Heaven," while calling for prayer for the conversion of sinners.
Mary appeared eight times to Mariette Beco, aged 11, outside the family home at Banneux, a small village, in Belgium [in 1932]. She described herself as the "Virgin of the Poor," and promised to intercede for the poor, the sick and the suffering.