The September 11, 2001, terrorist attacks stunned Americans. They also created new and unprecedented challenges for public administration, in theory and practice. A careful look at these challenges, however, reveals a familiar core: At its foundation, homeland security is about one of public administration's oldest puzzles—coordination. Although the field has a great deal to say about solving this puzzle, homeland security introduces new and especially difficult dimensions: matching place-based problems with functionally organized services; defining and achieving a minimum level of protection that all citizens ought to receive; building a reliable learning system for problems that, with luck, occur only rarely; balancing the new homeland security mission with existing missions that remain important; and meeting citizens' expectations in a fragmented governance system. These challenges demand a new, more effective system of contingent coordination, one that flexibly develops and matches government's capacity to new and unpredictable problems.