When building 3D mapping apps, we no longer have to deal with closed feature-sets, limited programming models, temporal data challenges and bulky deployments. This talk introduces Cesium, a WebGL-based JavaScript library designed for easy development of lightweight web mapping apps. With live demos, we will show Cesium's major geospatial features including high-resolution global-scale terrain, map layers and vector data; support for open standards such as WMS, TMS and GeoJSON; smooth 3D camera control; and the use of time as a first-class citizen. We will show how Cesium easily deploys to a web browser without a plugin and on Android mobile devices.Since last year's talk at FOSS4G NA, Cesium has added 3D models using the open-standard glTF, a large geometry library and higher-resolution terrain.