Inclinometers are devices used to measure changes in the inclination of measuring tubes that have been previously installed in the ground, rock mass, or geotechnical structures. The measured change in the inclination of the measuring tube can, under appropriate conditions, be interpreted as horizontal or vertical displacement. There are two versions of inclinometers: vertical and horizontal inclinometers. Vertical inclinometers monitor horizontal displacements. They are most commonly used in landslides and are crucial for understanding landslide mechanics, determining the depth of the slip plane, monitoring the magnitude, speed, and direction of the movement of the sliding mass, and verifying and proving the stability of slopes and retaining structures. Horizontal inclinometers monitor vertical displacements, such as ground settlement during the consolidation process. Monitoring settlement is especially important in embankment construction projects. The work also includes examples of inclinometer measurements from practice. The use of inclinometers in accordance with industry standards and good engineering practice reduces risks in geotechnical operations and enables the implementation of safe, high-quality, and rational design solutions.