This document reflects the themes and concepts developed in the accompanying Understanding Risk Communication Best Practices: A Guide for Emergency Managers and Communicators. This report discusses and dissects theories and models relevant to federal, state, and local homeland security personnel and emergency managers faced with communicating risks within their communities. It first provides a detailed discussion on defining risk communication, followed by risk characteristics to summarize how perceived dread and familiarity can affect risk messaging. Next, relevant theories and models1 are discussed in two parts: cross-cutting theories and models applicable across the preparedness, response, and recovery phases, and then additional theories and models that are most relevant within a specific event phase. As with the Best Practices document, many of the communication approaches presented were not originally designed for a specific event phase, but nevertheless offer valuable insights that make them particularly suitable for a specific event phase.