Three decades of the OGLE survey

. The Optical Gravitational Lensing Experiment (OGLE) is one of the most extensive sky surveys on a global scale. It focuses on optical astrophysical variability and is carried out using the dedicated 1.3-meter Warsaw Telescope located at Las Campanas Observatory in Chile. Since 1992, the OGLE project has been continuously observing the densest regions of the southern sky, namely, the Galactic bulge, Galactic disk, and Magellanic Clouds. To date, the survey has collected over a trillion individual photometric observations for approximately two billion stars. Throughout its long history, the OGLE project has yielded significant contributions to various fields of astrophysics, including gravitational lensing and microlensing, dark matter, exoplanets, variable stars, the structure of the Milky Way and other galaxies, and more. This article presents the most significant achievements of OGLE over the past 30 years.