This document provides an overview of ecosystems and the relationships between living and non-living components. It defines an ecosystem as including all the organisms and non-living factors in an area interacting as a functional unit. It describes different ecosystem types and sizes, from small piles of leaves to the entire biosphere. Key abiotic factors that determine what organisms can survive in an ecosystem, like soil, temperature, water, and sunlight, are also outlined. Relationships within ecosystems, like populations of the same species and communities of interacting populations, are examined.