In a unitary state, the central or national government has complete authority over all other political divisions or administrative units. For example, the Republic of France is a unitary state in which the French national government in Paris has total authority over several provinces, known as departments, which are the subordinate administrative components of the nation-state. The local governments of a unitary state carry out the directives of the central government, but they do not act independently.
The federal system of political organization is the exact opposite of the unitary state. For example, in contrast to the unitary state of France, Germany is a federal republic, which means that the national or federal government in Berlin shares political authority with the governments of several Lander, or political units within the nation-state. However,as in all federal states, including Australia, India, and the United States of America, the central or national government of Germany is supreme within the sphere of authority granted to it through the constitution.
Unitary states, like federal states, can be constitutional democracies or unfree non-democracies. Both the unitary Republic of France and the Federal Republic of Germany, for example, are constitutional democracies, but the unitary states of Algeria, Libya, and Swaziland are unfree non-democracies. The Republic of Sudan is an example of an unfree and non-democratic federal state.
By John Patrick, Understanding Democracy, A Hip Pocket Guide (Oxford University Press)