In classical Reformed thought, justification and righteousness fall within the parameters of "bi-covenantalism." This is roughly how the story goes: (1) our very great grandfather Adam, who corporately represented all of humankind, disobeyed God's law which brought a curse upon the earth or "imputed" his sin to all of us; (2) God then sends Jesus, who, like Adam, represents all humankind but, unlike Adam, was fully obedient. His "passive obedience" on the cross resulted in the sins of the members of the church (for those who adhere to limited atonement) being paid in full. His "active obedience" (i.e., His sinless life or "righteousness") fulfilled the law and is imputed to us as well; (3) Thus, Christians are relieved of the unpayable debt of sin by Christ's substitutionary atonement on the cross and then declared "righteous" by way of Christ's obedience and our faith in Christ. This is the great Reformed doctrine of "Justification by Faith Alone."
The first schema involving Adam (and Israel) falls within a covenant of works (i.e., obedience = blessing and disobedience = a curse) while the second system is a covenant of grace (i.e., because we cannot pay the price, Jesus pays it for us and because we cannot obey, Jesus obeys and imputes his righteousness to us).
I am in the midst of re-reading all of Bishop N.T. Wright's works in order to outline his theology in full. Included in this outline will be his controversial re-definition of "Justification" and "Righteousness." Check back soon and God bless!