The article provides a comprehensive overview of the development and applications of NOAA's Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model over the past three decades. HYSPLIT is a widely used atmospheric transport and dispersion model that calculates air parcel trajectories, transport, dispersion, chemical transformation, and deposition. The model has evolved from simple trajectory calculations based on radiosonde observations to a sophisticated system capable of simulating complex atmospheric processes. Key advancements include the integration of meteorological data from various sources, the inclusion of chemical transformations, and the development of multiple Lagrangian representations (3D particles, puffs, and hybrid approaches). HYSPLIT has been applied to a wide range of scenarios, such as tracking radioactive material, wildfire smoke, wind-blown dust, pollutants from various sources, allergens, and volcanic ash. The model's performance is evaluated using atmospheric tracer experiments, and it is widely used for operational forecasting, research, and public information dissemination.The article provides a comprehensive overview of the development and applications of NOAA's Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model over the past three decades. HYSPLIT is a widely used atmospheric transport and dispersion model that calculates air parcel trajectories, transport, dispersion, chemical transformation, and deposition. The model has evolved from simple trajectory calculations based on radiosonde observations to a sophisticated system capable of simulating complex atmospheric processes. Key advancements include the integration of meteorological data from various sources, the inclusion of chemical transformations, and the development of multiple Lagrangian representations (3D particles, puffs, and hybrid approaches). HYSPLIT has been applied to a wide range of scenarios, such as tracking radioactive material, wildfire smoke, wind-blown dust, pollutants from various sources, allergens, and volcanic ash. The model's performance is evaluated using atmospheric tracer experiments, and it is widely used for operational forecasting, research, and public information dissemination.