As sensor network deployments grow and mature there emerge a common set of operations and transformations. These can be grouped into a conceptual framework called Sensor Web. Sensor Web combines cyber infrastructure with a Service Oriented Architecture (SOA) and sensor networks to provide access to heterogeneous sensor resources in a deployment independent manner. In this chapter we present the Open Sensor Web Architecture (OSWA), a platform independent middleware for developing sensor applications. OSWA is built upon a uniform set of operations and standard data representations as defined in the Sensor Web Enablement Method (SWE) by the Open Geospatial Consortium (OGC). OSWA uses open source and grid technologies to meet the challenging needs of collecting and analyzing observational data and making it accessible for aggregation, archiving and decision making.