A method, system, and computer-readable medium is described for facilitating interactions between task requesters who have tasks that are available to be performed and task performers who are available to perform tasks. In some situations, the tasks to be performed are human performance tasks that use cognitive and other mental skills of human task performers, such as to employ judgment, perception and/or reasoning skills of the human task performers. In addition, in some situations the available tasks are submitted by human task requesters via application programs that programmatically invoke one or more application program interfaces of an electronic marketplace in order to request that the tasks be performed and to receive corresponding results of task performance in a programmatic manner, so that an ensemble of unrelated human agents can interact with the electronic marketplace to collectively perform a wide variety and large number of tasks.