Declarative query interfaces for Sensor Networks (SN)have become a commodity. These interfaces allowaccess to SN deployed for collecting data usingrelational queries. However, SN are not confined todata collection, but may track object movement, e.g.,wildlife observation or traffic monitoring. Whilerelational approaches are well suited for datacollection, research on Moving Object Databases (MOD)has shown that relational operators are unsuitable toexpress queries on object movement, i.e.,spatio-temporal semantics. The properties of SNprevent a straightforward application of MOD, e.g.,node failures, limited accuracy etc. Furthermore, MODmodel entities like regions as point sets whichpresumes very accurate knowledge on thespatial extend of these entities. Such knowledge isunavailable in most SN. Thisdissertation is the first to address spatio-temporalqueries in SN. It defines a complete set ofspatio-temporal operators for SN while taking intoaccount their properties and systematically shows howto derive query results from object detections.Finally, the dissertation presents a distributed,energy-efficient query processor for spatio-temporalqueries in SN.