This document discusses the disparate impact theory, which prohibits policies that disproportionately and adversely impact protected classes. It summarizes that the theory is important because it brings life to fair housing acts, addresses unintentional discrimination, and combats systemic discrimination. The theory has been upheld by courts, enforced by HUD, and used by the Department of Justice to address issues like redlining, reverse redlining, discrimination, lending discrimination, and holding Wall Street accountable. The document outlines how to build a case using disparate impact theory and addresses issues and limits around its use.