Freezing and thawing processes of soils have a significant impact on energy and water transfer between the atmosphere and the land surface, surface hydrology, agriculture, carbon cycle, and ecosystem as a whole. The timing, duration, areal extent, and depth of surface soil freezing and thawing are important parameters for regional climatic and hydrologic studies, and changes in these parameters are also important climatic indicators. In this study, the timing, duration as well as the number of days, and extent of surface soil freeze/thaw cycle were investigated using passive microwave satellite remote sensing data combined with ground-based measurements and numerical modeling in the contiguous United States. Three different algorithms were validated against ground-based measurements from more than 20 stations throughout the contiguous United States over two years. Different cut-off brightness temperatures in three algorithms were used to account for different land surface type and vegetaion. Results indicate that frozen soil algorithms can predict the near-surface soil freeze/thaw cycle with accuracy of 90% or better for bare land surface. Over the vegetated areas, the accuracy ranges from 60% to 90%, depending on vegetation type and fraction in each pixel. Generally, The onset of surface soil freezing starts in October or November at high latitude/altitude regions and in December or even January over middle latitude lowlands. The last day of surface soil freezing ranges from February or March in middle latitude regions to April or May at high latitude/altitude regions. These results show that the duration of surface soil freezing varies from a few weeks to several months. The number of days that surface soil actually experiences freeze/thaw cycles varies from a few days to more than five months. Surface soil experiences freezing before snow covers the surface. However, the frozen soil may disappear quickly after a steady snow cover is established over the freezing surface, especially in the middle latitudes. For the period from 1988 through 2000, approximately 60% to 80% of the land area in the contiguous United States experienced freeze/thaw cycles. The long-term (1988-2000) trends of snow cover, the timing, duration, and number of days of the near-surface soil freeze/thaw cycle and their relationship with climatic conditions will also be discussed in this presentation.