Over the last two decades, international human rights instruments, decisions, and dedicated advocates have advanced the understanding of domestic violence. Once considered a private act committed with widespread impunity, domestic violence is now viewed as a human rights violation that states have a responsibility to address. This article will trace the history of this progression and the emergence of a "due diligence" standard to assess a state's response to domestic violence. The first half of the article will examine the recognition of the due diligence standard as a rule of customary international law with increasingly defined state obligations. The second half of the article will analyze the evolution of the due diligence standard within the European Court of Human Rights (ECHR) and the application of the standard in two landmark cases, and both cases held national governments responsible for failing to exercise due diligence to adequately protect individuals from domestic violence. The decisions in these cases not only affirm the use of the due diligence standard as a tool for assessment, but also they begin to clarify the practical obligations of protecting victims from domestic violence as well as preventing, investigating, and prosecuting such violence. In particular, the ECHR highlights the need for enforceable measures of protection and a legislative framework that enables criminal prosecutions of domestic violence in the public interest. Furthermore, the article will analyze the decision in, and the Court's recognition that, a State's obligation to exercise due diligence to protect women against domestic violence is gender-based discrimination, violating women's right to equal protection of the law.