Soil Moisture (SM), being one of the main variables within the system that controls the hydrological interactions among soil, vegetation and atmosphere, plays a key role in the water cycle. Satellite systems, both active and passive, have already demonstrated their capability to provide reliable SM measurements. The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission, launched in November 2009, was the first specific SM satellite mission. In this work we assessed the capability of SMOS data to accurately capture SM dynamics over a long time period by comparing them with in situ observations. To better assess the performance of such results, they were also compared with those obtained with alternative satellite-based SM products, considering in particular those generated by Advanced Microwave Sounding Radiometer (AMSR-E) and Advanced SCATterometer (ASCAT) data.