De-democratization may take the form of executive-led attacks as well as incremental decrepitude, gradual emptying of underlying constitutional values, and state inertia. Contrary to general wisdom, both exogenous erosion and endogenous decay are heavily affected by informality. As courts are often the first institutions affected by de-democratization, this Article analyzes informality in erosion and decay of judicial institutions. It argues that such institutions interact with democracy in two core directions. The first one is endogenous and describes the decay of democratic judiciaries as a result of a long-term incongruence between formal and informal judicial institutions. The second direction captures the gradual erosion of informal institutions that have positive effects on judicial democratic resilience. These two processes, decay and erosion of informal judicial institutions, should not be overlooked. While they are less visible, slower, and often unintentional, they are as dangerous as frontal executive-led attacks on courts, because they significantly increase the window of opportunity for politicians who wish to downgrade the substance of democracy or even implement a regime change.