Accurate and timely information on crops is essential for national and regional food security, market planning, and social stability. All stakeholders (e.g., decision makers, traders, farmers) need reliable and up-to-date crop monitoring information whenever and wherever possible. A comprehensive online platform for global crop monitoring ought to be established to provide customers with a variety of real-time, easily accessible, and efficient services, such as raw data, information, maps, and analytical tools. The emergence of cloud computing provides a good opportunity to build such a global crop monitoring instrument. After a detailed inventory of the status, scope, and technological basis of existing cloud and remote sensing-based global crop monitoring systems, this study focuses on the relevance of CropWatch Cloud. The basic design concept, design framework, and main contents of CropWatch Cloud service platform are described, which will incorporate expert knowledge, advanced IT technology, and data resources. A virtuous cycle will be built to bridge science, technology, services, and applications. A prototype of CropWatch online was developed; users can query and download time series of crop monitoring indicators at different scales. The prototype of CropWatch online is an important part of CropWatch Cloud; it provides a downloading service for crop information, also stores and manages a long-term series of crop monitoring data and results. The evolvement of a local crop monitoring application into a convenient web-based application with multiple-terminal support is the key of the CropWatch Cloud project. The developed design framework will provide theoretical guidance and a sound basis for the construction of the CropWatch Cloud service platform. This platform will change the application patterns and promote the industrialization of agricultural remote sensing monitoring.