In this lecture from the Yale Quantum Institute Course on Quantum Error Correction, held at Yale University in July 2025 in partnership with North Carolina A&T, Daniel Weiss introduces bosonic modes and the Kraus operator formalism used to describe how quantum systems interact with their environment and lose information through noise. The lecture connects this mathematical machinery to practical error models relevant to superconducting quantum hardware. It follows the course's earlier sessions on classical and quantum error correction and stabilizer codes, building the tools needed to understand the physical origins of errors that the correction schemes are designed to address.