This paper provides an overview of sensor webs from the perspective of Earth observation. Definitions of in-situ, proximal, and remote sensing are presented. Sensor webs are also defined and the over-arching concept of integrated Earth sensing is outlined. The paper goes on to describe experiences in the development and deployment of sensor web prototypes in support of vegetation monitoring applications. Recommendations are provided with regard to where the emphasis should be placed for advancing in-situ sensor webs in the context of Earth observation in the future. Finally, the geostrategic importance of integrated Earth sensing, sensor webs and related technologies is discussed.