FEMA's Mission: Policy Directives for the Federal Emergency Management Agency [Updated March 13, 2002] [open pdf - 160KB]
"The Federal Emergency Management Agency (FEMA) assists states and localities overwhelmed by, or at risk from, disasters. FEMA also coordinates federal emergency management activities and planning for the continuity of government should national security be threatened. [...] This report identifies authorities drawn from public sources. It does not refer to classified authorities not available to the public, does not include references to temporary authorities that require FEMA to provide assistance for specific disasters or needs, and does not include information on plans, regulations, or operating manuals developed to implement these policies."
CRS Report for Congress, RL31285