This chapter explores the foundational concepts and architectural frameworks underpinning geospatial digital twins—dynamic, virtual replicas of physical systems that integrate spatial data, sensor networks, simulation models, and analytics. It begins by synthesizing definitions from leading organizations such as Esri, 1Spatial, EuroSDR, and ISPRS, revealing a common understanding of geospatial digital twins as spatially anchored, temporally aware systems that reflect and influence real-world environments. The chapter then introduces a multi-perspective architectural analysis, classifying digital twin architectures along five dimensions: scale, function, sector, data fidelity, and integration depth. Each dimension is unpacked with real-world case studies and architectural component summaries, culminating in a synthesized framework that balances standardization with domain-specific flexibility. The case study of Singapore’s “Virtual Singapore” provides a practical illustration of how these architectural principles converge in a national-scale implementation. Ultimately, the chapter establishes geospatial digital twins not merely as technical systems, but as transformative infrastructures for cross-domain decision-making, real-time monitoring, and predictive planning across urban, environmental, and economic landscapes.