In every modern political system, power is shared to a greater orlesser extent between levels of government. These power sharingarrangements are perhaps most explicit in formal federal systemslike the United States and Canada, where federal constitutionsdefine the relative powers of central and subnational governments.They may be no less important, however, in unitary democracies andeven authoritarian regimes where central governments require localactors to implement policy on the ground and often delegatesignificant authority to them. Indeed, in any large and complexmodern society, effective governance requires some sharing of powerbetween higher levels of government, capable of coordinating manydisparate actors and interests, and lower levels of government,capable of responding to local conditions.