The sea level is monitored in-situ and pointwise using tide gauges, or remotely and globally using satellite altimetry techniques. Tide gauges measure sea level relatively to the ground, thus they register also ground motions. To infer sea level changes with high reliability, the vertical land motion needs to be subtracted. In the analysis of historical tide gauge data, only effects of the Glacial Isostatic Adjustment (GIA) are considered. In analysis based on recent data, the vertical land motion at tide gauge locations is determined with GNSS positioning. Although the GNSS-based vertical land motions represent short time intervals (5 to 20 years only), it is usually assumed that they represent long-term trends. Different studies based on historical or reconstructed tide gauge data agreed on a mean rate 20th century sea level rise in the range of 1.6 to 1.8 mm/yr.