Techniques are described for managing execution of programs on multiple computing systems, such as based at least in part of user-specified constraints. For example, constraints related to execution of a program may be based on a desired relative location of a host computing system to execute a copy of the program with respect to an indicated target (e.g., computing systems executing other copies of the program or copies of another indicated program), on particular geographic locations, and/or on factors not based on location (e.g., cost of use of a particular computing system, capabilities available from a particular computing system, etc.). Some or all of the multiple computing systems may be part of a program execution service for executing multiple programs on behalf of multiple users, and each may provide multiple virtual machines that are each capable of executing one or more programs for one or more users.