The Unitroller is the risk management layer of the Fortress protocol. It determines how much collateral a user is required to maintain, and whether a user can be liquidated. Each time a user interacts with fToken, the Unitroller is asked to approve or deny the transaction. The Unitroller maps user balances to price to asses risks (collateral factors) and to make determinations. Users explicitly list which assets they would like included in their risk scoring, by calling EnterMarkets and ExitMarket.