Biomonitoring is the practice of using samples of resident organisms to determine ecosystem health or condition. This basic concept has been applied to diverse ecosystems, organisms, and stressors. Standardized protocols for freshwater biomonitoring have been established all over the world, including the methods used for community-based monitoring. Yet, how specific invertebrates are selected and incorporated into biotic indices can seem arbitrary. By exploring the ecology of freshwater invertebrates, we can better appreciate their contributions to freshwater ecosystems as well as their role in biomonitoring.