Abstract: Application virtualization at the thread level, rather than at the process level. the operation of a thread across virtualization contexts. For instance, one virtualization context might be a native environment, whereas another virtualization context might be a virtualization environment in which code running inside a virtualization package has access to virtualized computing resources. A thread operating in a first virtualization context then enters an entry point to code associated with a second virtualization context. For instance, a native thread might enter a plug-in operating as part of a virtualized package in a virtualization environment. While the thread is operating on the code, the thread might request access to the second computing resources associated with the second virtualization environment. In response, the thread is associated with the second virtualization context such that the thread has access to the second computing resources associated with the second virtualization context.