Extreme wildfire events in recent years are shaking our established knowledge of how fire regimes respond to climate variables and how societies need to react to fire impacts. Albeit fires are stochastic and extreme in nature, the speed, intensity, and extension of new extreme fires that have occurred during the last years are unprecedented. Here, we identify common features of these emerging novel extreme wildfire events characterized by very high fire intensity and rapid rates of spread, and we review the major mechanisms behind their occurrence. We then point to the major challenges that extreme wildfire events pose to science and societies worldwide, both today and in the future. Climate change and other factors are contributing to more flammable landscapes and the promotion of unstable atmospheric conditions that ultimately promote wildfire development. Anticipating these novel conditions is a key scientific challenge with paramount implications for present and future fire management, ecosystems, and human well-being.