Communication between program components executing in different virtual machines on the same physical computer may be optimized utilizing various mechanisms. A virtual machine manager may be configured to route network communications between virtual machines on the same physical host through a memory buffer. The virtual machine manager might also be configured to provide a shared memory and/or a shared data structure for enabling data communication between program components executing in different virtual machines on the same physical computing device. Mechanisms might also be implemented in order to prevent inconsistent read and/or write operations from being performed on the shared memory and/or the shared data structure. Mechanisms might also be implemented to minimize copying of a memory buffer, shared memory, and/or shared data structure.