A core function of a central bank is to support financial stability, including acting as lender of last resort to the banking system. This means that when a solvent bank or financial institution faces a temporary liquidity shortage and cannot obtain sufficient funding from normal market sources, the central bank may provide emergency liquidity to prevent the problem escalating into a wider loss of confidence, bank runs, or systemic disruption. This role is distinct from day to day commercial decisions. Central banks do not guarantee the success of individual businesses, and they do not make lending decisions for individual banks, which remain responsible for credit underwriting and risk management. Central banks influence the level of interest rates in the economy through policy rates and monetary operations, but they do not directly set mortgage rates, which are determined by banks based on funding costs, competition, risk, and policy expectations. For CISI purposes, the cleanest and most examinable statement is that central banks act as lender of last resort, alongside their broader responsibilities for monetary stability and supporting the payment and banking system.