Assets whose fair value cannot be determined by using observable measures, such as market prices or models. Level 3 assets are typically very illiquid, and fair values can only be calculated using estimates or risk-adjusted value ranges. In addition to Level 1 and Level 2 assets (both of which have more accurate fair values), Level 3 assets must be reported on by all publicly traded companies as of 2008.

This classification system came about as a result of FASB Statement 157, which aims to bring clarity to the balance sheet assets of corporations. Even though they are hard to value, Level 3 assets are held at large investment shops and commercial banks by the billions.

These assets received heavy scrutiny during the credit crunch of 2007, as many Level 3 assets consist of mortgage-backed securities (which suffered massive defaults and write-downs in value). The firms that owned them were often not adjusting asset values downward even though credit markets had dried up in the market for asset-backed securities, and all signs pointed to a decrease in fair value.