‘Federalism’, in general usage, describes a method of political organization in which two levels of government have constitutional power to legislate and govern; one level governs with respect to the country as a whole, the others with respect to one of the provinces or states that make up the federation.
The virtue of federalism is that it makes possible the union of regions and peoples with certain shared interests and objectives, but with significant differences in culture, language, religion or history. That is, it allows these divergent groups to achieve union for the shared purposes while permitting regional governments to act for the differing characteristics and interests. The constitution of a federation must be written to provide certainty, with a court of law to interpret it in cases of conflict or difference.
To protect the agreed distribution of the powers (see division of powers) of government, any amendment of a federal constitution normally requires a special level of agreement by the population or by the constituent governments or by both (see amending formula).
In addition to these features, a successful federal system must provide protection for the less populous regions and peoples through a second legislative chamber in the central parliamentary institution. This is normally provided by having a special basis of election or appointment for that chamber other than representation by population.
As it is not possible to devise a distribution of governmental powers without overlap or dispute as to jurisdiction, provision must be made or must develop for collaboration between the two levels of government (see concurrency).
 Peter W Hogg, Constitutional Law of Canada, Student ed 2005 (Toronto: Thomson Carswell, 2005) at 106-117.
 RL Watts, Comparing Federal Systems, 2d ed (Kingston: Published for the School of Policy Studies, Queen’s University by McGill-Queen’s University Press, 1999) at 4.
 See: JR Hurley, Amending Canada’s Constitution: History, Processes, Problems and Prospects (Ottawa: Privy Council Office, Policy Development and Constitutional Affairs, 1996).
 Comparing Federal Systems, supra note 2 at 57-61.