This chapter explains the two categories of QC checks followed in handling meteorological data, viz. static and dynamic for a variety of observation types, including the surface, radiosonde data. The static QC checks are single-station, single-time checks which, as such, are unaware of the previous and current meteorological or hydrologic situation described by other observations and grids. Dynamic checks, which refine the QC information by taking advantage of other available meteorological information, are used. Examples of dynamic QC checks include position consistency, temporal consistency, and spatial consistency.