Per user file associations

Systems and methods are provided for defining a default handler software application in response to an event at a computer. An event, for example, a user opening a file with a specific extension or accessing a uniform resource locator (URL) with a specific protocol, may trigger the operating system to instantiate a user-level default handler program associated with the event type and the specific user. Users may define user-level default handlers through a centralized user interface maintained by the operating system. During the application installation process, an application may register lists of supported events that the application is capable of handling.