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Bound states in the continuum (BICs) have attracted attention in photonics owing to their interesting properties. For example, BICs can effectively confine light in a counterintuitive way, and the far-field radiation of photonic structures that exhibit BICs has fascinating topological characteristics. Early research into photonic BICs was primarily focused on designing artificial structures to produce BICs. However, since the mid-2010s, exploring the potential applications of BICs has been a growing trend in research. In this Review, we detail the unique properties of BICs, including the ability to achieve enhanced light confinement, sharp Fano resonances and topological characteristics. We explore phenomena derived from BICs, including the generation of circularly polarized states and unidirectional guided resonances, and the impact of BICs on various applications such as lasing, nonlinear frequency conversion …