Oda of Haldensleben (c. 955/60 – 1023) was a German noblewoman and by marriage Duchess of the Polans.
She was the eldest child of Dietrich of Haldensleben, Margrave of the North March.
By most accounts, she grew up in the monastery of Kalbe, near to Milde river in the north of Magdeburg. Eventually she became a nun there, but c. 978/79 she was abducted by Duke Misaca (Mieszko I of Poland) (who had lost his first wife, the Bohemian princess Dobrawa in 977) and married soon after. This union produced three sons:
- Mieszko (born c. 979 – died after 992/95).
- Świętopełk (born c. 980 – died before 991?).
- Lambert (born c. 981 – died after 992/95).
Some 80 years later a reference in an obscure church book mentions "Ote and Dago(me)". There is no actual document and the church book mentioning from c. 1080 is known as Dagome iudex and thus assumed to be one of the earliest Polish legal documents. It's a principal source for this portion of the history of Poland under the Piast Dynasty.
The undated mentioning from 1080 states that (shortly before his death?) "Dago(me)" (assumed to be Mieszko I) gifted his territory to Pope John XV and received his domains from him as a fief in this Dagome iudex, not date, apparently issued shortly before his death, c. 991/92. This document indexes the lands of (Mieszko), referred to as "Dagome" in the document, and his wife "Ote" and her sons by him (Mieszko and Lambert are only named; probably Świętopełk was already dead by that time or was in Pomerania as a ruler, according to modern historians).
Mieszko I's oldest son, Bolesław I the Brave, is not mentioned, perhaps because he already received his inheritance (probably Lesser Poland, who included Kraków and some other cities). It's also believed that the document was inspired by Oda, who wanted to secure the inheritance of her sons (with the Papal protection) in detriment of her stepson Bolesław I.
After the death of Mieszko I (25 May 992), Bolesław I began the struggle against his half-brothers for the control over the paternal heritage. According to some historians, the war lasted only a few weeks, and according to others, only finished around 995, when Bolesław I expelled his stepmother and half-brothers from Poland and took control over all Mieszko I's domains.
Oda returned to Germany and entered in the Abbey of Quedlinburg as a nun, where she died almost thirty years after her husband, in 1023. Nothing is known about the fate of her sons, but in 1032 her grandson Dietrich or Dytryk (son of either Mieszko or Lambert) returned to Poland and obtain parts of the country after the fall of Mieszko II Lambert; however, one year later he was expelled by Mieszko II, who could again reunite The Poland in his hands.