Natural justice principles demand impartial decision makers and a fair hearing to prevent perceived bias and protect interests. Principles of natural justice require impartial decision makers and a fair hearing before actions affecting rights, livelihood, liberty, property or legitimate expectations; the core rules are nemo judex in causa sua and audi alteram partem. The bias inquiry focuses on whether a reasonable observer would perceive a real likelihood of bias, and what procedural fairness requires depends on the nature of the power, the interests affected, the statutory context, and whether the function is judicial, quasi judicial, disciplinary or administrative.