Project Reassimilation was a Starfleet operation to study recovered Borg technology with the intention of reverse engineering it and applying it to Starfleet purposes.

Following the Borg Invasion of 2381, Lieutenant Commander Kareem Mussad and his Starfleet Corps of Engineers team on Deep Space 3 took possession of at least seventy-four samples of Borg technology for study as part of Project Reassimiliation. This was done under strict security protocols, ordered by Starfleet Security, with only the SCE team and the station's commanding officer, Commander Gong, aware of the study. Unfortunately, all recovered material had been rendered inoperative by the Caeliar's transformation of the Borg.

Among those working on Project Reassimiliation under Mussad were Ensign Xi and Lieutenant Baldvinsson. Mussad reported directly to Starfleet Corps of Engineers Command Liaison Montgomery Scott. (ST novel: A Singular Destiny)

It is likely that Starfleet's study of Borg remains had been ongoing since their earliest encounter, whether under the name "Project Reassimilation" or not. However, the work being done on DS3 was apparently started only after the invasion.