Durability is an essential feature of most elastomer products, directly linked to safety and to perceptions of brand quality. Product designers must therefore consider the impact on product durability of typical and abusive end-user loading scenarios. This can be accomplished using critical plane analysis (CPA). CPA starts by acknowledging that a small crack precursor might exist at any point in a part, and in any orientation, and that the potential development of all crack precursors must be evaluated. The analysis produces a full accounting of which location and orientation maximizes crack growth (or, equivalently, minimizes fatigue life) at each point, the energy release rate history experienced, and of course the worst-case fatigue life across all possible orientations. This review provides an account of the development of the method over the last two decades and the validation case that has accumulated. This review also suggests directions for further development of the method.