The article discusses the significance of long-period (LP) seismicity in active volcanoes, which reflects pressure fluctuations in the sub-surface plumbing system. LP seismicity, characterized by periods ranging from 0.2 to 2 seconds, can indicate impending eruptions when it occurs at shallow depths. The science of volcano seismology aims to understand the dynamics of active magmatic systems and map the extent and evolution of source regions of magmatic energy. LP events and tremor are distinct but share common temporal and spectral characteristics, suggesting a common source process. LP activity is particularly useful for eruption forecasting due to its potential to reveal the physical processes that generate it. The article reviews the identification and discrimination of LP events from other types of seismic activity, such as volcano-tectonic (VT) earthquakes, and discusses the importance of source modeling to understand the underlying mechanisms. It highlights the role of LP activity in monitoring the internal state of volcanoes and the challenges in understanding deep LP events. The article concludes by emphasizing the need for further research to improve the understanding of LP activity and its relationship with volcanic processes.The article discusses the significance of long-period (LP) seismicity in active volcanoes, which reflects pressure fluctuations in the sub-surface plumbing system. LP seismicity, characterized by periods ranging from 0.2 to 2 seconds, can indicate impending eruptions when it occurs at shallow depths. The science of volcano seismology aims to understand the dynamics of active magmatic systems and map the extent and evolution of source regions of magmatic energy. LP events and tremor are distinct but share common temporal and spectral characteristics, suggesting a common source process. LP activity is particularly useful for eruption forecasting due to its potential to reveal the physical processes that generate it. The article reviews the identification and discrimination of LP events from other types of seismic activity, such as volcano-tectonic (VT) earthquakes, and discusses the importance of source modeling to understand the underlying mechanisms. It highlights the role of LP activity in monitoring the internal state of volcanoes and the challenges in understanding deep LP events. The article concludes by emphasizing the need for further research to improve the understanding of LP activity and its relationship with volcanic processes.