Sea level is monitored in Spain by various agencies for different applications: control of the national levelling system, oceanographic studies, climate change, operational purpose, harbour operations, navigation, etc. A general overview of the Spanish sea level networks is presented in this paper, as well as the new strategy that is being discussed for the ongoing sea level monitoring system in Spain. The sea level data for the period 1990-1999 is examined and general information about the mean sea level evolution during that decade. Seasonal variability and tides are presented.