API Reference > core-frontend > IModelApp IModelApp Classes for configuring and administering an iTwin.js application. See the learning articles. Classes Name Description IModelApp Global singleton that connects the user interface with the iTwin.js services. Constants Name Description iModelJsCss ITWINJS_CORE_VERSION Interfaces Name Description FrontendSecurityOptions Options that can be supplied with IModelAppOptions to customize frontend security. IModelAppOptions Options that can be supplied to IModelApp.startup to customize frontend behavior. Last Updated: 18 May, 2022