The following represent a high-level overview of Windows Installer:

• Transactional operations: All installation operations are transactional. For each operation that Windows Installer performs, it generates an equivalent undo operation that would undo the change made to the system. If a failure occurs during the middle of an installation, Windows Installer can roll back the machine to its original state.
• Self-healing: Windows Installer supports "self-healing" abilities for applications. Applications can detect common installation problems at launch, like missing files or registry keys, and automatically repair themselves.
• Installation on demand: Windows Installer supports on-demand installations of application features. For example, the spelling checker in Microsoft Office Word may not be installed by default, but a user can trigger an on-demand installation of this feature.
• Installation in locked-down environments: In fully locked-down environments, users don't generally have permission or the ability to install applications. In most cases, they don't have write-access to the Program Files folder of their computers or to the HKEY_LOCAL_MACHINE registry location. If an administrator approves an installation package by means of Group Policy, for instance, Windows Installer can perform an installation on the user's behalf.
• State management: Windows Installer provides a set of standard Win32® application programming interfaces (APIs) and automation interfaces for applications and administrators to use for querying the installation state on the machine. The APIs allow querying of the current state, verification of the existing state, repair of a corrupted state, and transition from one state to another.