This On-Scene Commander's Guide for Responding to Biological/Chemical Threats has been developed in coordination with "stakeholders" from federal agencies (the "interagency"), and state and local emergency responder communities. It was developed to enhance the previously disseminated guidance distributed as NDPO Bulletins distributed in December 1998 and April 1999. It is a tool to assist commanders in the field in assessing options during the first two hours of an incident involving a potential biological or chemical agent. It is intended to augment existing response policies and not supersede local protocols. This Guide is general in nature and not intended to be a technical guide for emergency responders. The Guide has dual applicability in law enforcement and public safety communities.