Hosts are typically coinfected by multiple parasite species, resulting in potentially overwhelming levels of complexity. We argue that an individual host can be considered to be an ecosystem in that it is an environment containing a diversity of entities (e.g., parasitic organisms, commensal symbionts, host immune components) that interact with each other, potentially competing for space, energy, and resources, ultimately influencing the condition of the host. Tools and concepts from ecosystem ecology can be applied to better understand the dynamics and responses of within-individual host–parasite ecosystems. Examples from both wildlife and human systems demonstrate how this framework is useful in breaking down complex interactions into components that can be monitored, measured, and managed to inform the design of better disease-management strategies.