Saint Adelaide of Italy (931-December 16, 999) was the daughter of Rudolf II of Burgundy, King of Italy. Her first marriage was to Lothar, King of Italy, and was part of a political settlement designed to conclude a peace between her father, Rudolf II, and Hugh of Provence, the father of Lothar.

The Calendar of Saints states that her first husband was poisoned by his successor, Berengar of Ivrea, who attempted to cement his political power by forcing her to marry his son; when she refused, she was imprisoned for four months, and escaped to Canossa, where she threw herself on the mercy of King Otto I the Great; they subsequently married in 951 .
They had four children:
- Henry, born in 952;
- Bruno, born 953;
- Matilda, Abbess of Quedlinburg, born about 954; and
- Otto II, later Holy Roman Emperor, born 955.

When her husband Otto I died in 973 he was succeeded by their son Otto II, and Adelaide for some years exercised a powerful influence at court. Later, however, her daughter-in-law, the Byzantine princess Theophano, turned her husband against his mother, and she was driven from court. Finally a reconciliation was effected, and in 983 Otto appointed her his viceroy in Italy. However, Otto died the same year, and although both mother and grandmother were appointed as co-regents for the child-king, Otto III, Theophano forced Adelaide to abdicate and exiled her. When Theophano died in 991, Adelaide was restored the regency of her grandson. She was assisted by Willigis, bishop of Mainz. In 995 Otto III came of age, and Adelaide was free to devote herself exclusively to works of charity, notably the foundation or restoration of religious houses.

Adelaide had long entertained close relations with Cluny, then the center of the movement for ecclesiastical reform and in particular with its abbots Majolus and Odilo. She retired to the convent of Seltz near Cologne. Though she never became a nun, she spent the rest of her days there in prayer. On her way to Burgundy to support her nephew Rudolf III against a rebellion, she died at a monastery she had founded Seltz in the Alsace on December 16, 999. She had constantly devoted herself to the service of the church and peace, and to the empire as guardian of both; she also interested herself in the conversion of the Slavs. She was thus a principal agent—almost an embodiment—of the work of the Roman Catholic Church during the Early Middle Ages in the construction of the religion-culture of western Europe. Her feast day is still kept in many German dioceses.