Judicial Review - Introduction1. History
Judicial review is a long-standing legal remedy that stands at the heart of the judiciary's role in our society. It is the essence of the s.96-constitutional role of the Superior Court. Historically legislatures have tried to limit, or even abolish, judicial review with 'privative' clauses (statutory provisions that purport to exclude the court's jurisdiction) - but the rule of the courts has prevailed, and so it must.
2. The Substantive Law
Central to Ontario's Judicial Review Procedure Act (JRPA) - and thus central to the Ontario law of judicial review (JR) - is s.2(1) [entitled "Applications for Judicial Review"]:
2(1) On an application by way of originating notice, which may be styled “Notice of Application for Judicial Review”, the court may, despite any right of appeal, by order grant any relief that the applicant would be entitled to in any one or more of the following:While s.2(1) is divided into two parts: 1. 'prerogative writs' [2(1)1], and 2. declarations and injunctions regarding 'statutory powers' [2(1)2], it essentially deals with one combined topic - public law. The meaning of 'public law' is most easily explained by it's contrast with 'private law' - ie. that of contract, tort, private property, estates and such. In a very accurate sense, 'public law' is all the law that isn't private law.
1. Proceedings by way of application for an order in the nature of mandamus, prohibition or certiorari.
2. Proceedings by way of an action for a declaration or for an injunction, or both, in relation to the exercise, refusal to exercise or proposed or purported exercise of a statutory power.
Another tempting alternative candidate to the term 'public law', is 'government law' but - despite ample oppourtunity to adopt it - the profession hasn't done that yet. What we find instead is a hodge-podge of indicia as set out in the leading Setia v. Appleby College (Ont CA, 2013) case:
 The assessment of whether a particular decision is subject to public law and its remedies requires a careful consideration of the relevant circumstances of the particular case informed by the experience of the case law. I agree with the approach of Stratas J.A. in Air Canada v. Toronto Port Authority,  F.C.J. No. 1725, 2011 FCA 347. He said this, at para. 60:3. The Procedural Law
There are a number of relevant factors relevant to the determination whether a matter is coloured with a public element, flavour or character sufficient to bring it within the purview of public law. Whether or not any one factor or a combination of particular factors tips the balance and makes a matter "public" depends on the facts of the case and the overall impression registered upon the Court. In his very helpful reasons, Stratas J.A., at para. 60, described a number of relevant factors disclosed by the case law:
-- the character of the matter for which review is sought;
-- the nature of the decision-maker and its responsibilities;
-- the extent to which a decision is founded in and shaped by law as opposed to private discretion;
-- the body's relationship to other statutory schemes or other parts of government;
-- the extent to which a decision-maker is an agent of government or is directed, controlled or significantly influenced by a public entity;
-- the suitability of public law remedies;
-- the existence of a compulsory power;
-- an "exceptional" category of cases where the conduct has attained a serious public dimension. [page490]
In Ontario, judicial review (JR) proceedings are usually (not always) advanced by a specific procedure, that of an 'application for judicial review' in the Divisional Court [JRPA 6(1)]. JR proceedings can be brought both in the Divisional Court (always as an application) or - more rarely, in the Superior Court (both as an application and an action).
When they are brought as an application [under R68] they are brought by a modified version of a standard Superior Court legal procedure, the 'application' [in it's non-JR version it's under R38]. 'Applications' - in normal Superior Court practice - are distinct from 'actions', the latter of which may be thought of as the standard lawsuit for such typical things as breach of contract or tort damages. Applications are proceedings of a simpler-evidentiary nature, normally heard on affidavit evidence only.
Then there are two distinct Superior Court routes by which JR procedures may be brought: the so-called 'urgent route' (which is an application) [JRPA 6(2)], and the little-used and misunderstood s.8 JRPA route (which I call the 'damage' route - it's an action). The criteria and details for the use of all of these three 'judicial review routes' are unpacked and explained in the 's.2 Procedural Options' section below.
It's worth noting that a party may attempt to file a 'regular' (non-JR) Superior Court proceeding and - to their surprise - have it treated as an 'application for judicial review' by the court, just by virtue of the party requesting judicial review remedies [JRPA 2(1) "which may be styled ", and JRPA 11(1)]. In other words - even if the applicant does not know it - it is the nature of the remedies sought that defines whether a party has commenced a JR proceeding, not the party's self-styled perception of the proceeding.
JRPA 11(1) - References in other Acts, etc.
4. Judicial Review is Discretionary Relief
It's part of the long history of judicial reviews that they are 'discretionary', and that this discretion applies to both their granting [JRPA 2(5)] and remedial aspects [JRPA 2(1) ("may")]. Another way of putting this is that the court may decline (with reason) to grant a JR application - even though the applicant may have technical grounds otherwise entitling them to it - and that even if an application is granted, the court may decline to order a remedy.
Lately I have come to think of the 'discretionary' nature of JRs as a function of their JRPA 2(1) remedies - being those of the prerogative writs, declarations and injunctions. These remedies are all, traditionally, equitable remedies which are by their nature discretionary. This logically renders them vulnerable to equitable defences, classically those of 'lack of clean hands' and similar. I haven't found any cases on this yet, but it's an interesting line of thought.
While it may seem a minor thing to make a point of at this introductory section, it's discretionary nature is at the heart of key current developments in JR law [see the 'adequate alternative remedy' [s.3] discussion and it's multiple modern cases].