Eustace was the elder son of Count Baldwin II of Boulogne and Adelina of Holland.
[2] In 1028 Eustace confirmed the foundation of a college of canons in his castle at Lens[2] and despite accounts of Lens passing to Baldwin V of Flanders circa 1036 it was still held by Eustace and was passed to his son Lambert at his death.
[4] In 995, having attained his majority, Baldwin IV attempted to recover several of the independently held castles and to expand the Flemish borders.
[6] This had far reaching alliances to other branches of these families including that of Edward the Confessor, King of England.
[6] Under Eustace the counts of Boulogne rose to great prominence in Northern France.