Abuse of Process1. General
2. Attempts at Defining Abuse of Process
3. Abuse of Process Contrasted with Issue Estoppel and Res Judicata
4. Abuse of Process in Relation to Other Doctrine
5. Abuse of Process and the Rules of Civil Procedure
1. GeneralAbuse of process is a new and relatively ill-defined doctrine, which to me indicates that it is a reflection of legal change. It has developed, and is developing, as a legal 'reason' for dealing with some underaddressed phenomenon of law. So trying to pinpoint it's essence is a bit of a mug's game right now, the easiest way to assess it right now is to just look for cases were judges have 'relied' up it, and characterize those situations.
So here goes.
2. Attempts at Defining Abuse of Process. Phillion v. Ontario (Attorney General)
In Phillion v. Ontario (Attorney General) (Ont CA, 2014) the Court of Appeal quotes from the Supreme Court of Canada on the elements of abuse of process, citing the close relationship that the doctrine has with issue estoppel, and the broad (even primordial) relation that it bears to 'justice':
 The leading case on the doctrine of abuse of process is the Supreme Court of Canada’s decision in Toronto (City) v. C.U.P.E., Local 79, 2003 SCC 63 (CanLII), 2003 SCC 63,  3 S.C.R. 77. Arbour J. explained, at paras. 35-37, that this doctrine represents the inherent and residual discretion to “prevent an abuse of the court’s process” when other doctrines such as issue estoppel may not be available. At para. 35, she adopted the words of McLachlin J. (as she then was) in R. v. Scott, 1990 CanLII 27 (SCC),  3 S.C.R. 979, at p. 1007, as follows:Again, in Phillion, the court commented generally on the nature of abuse of process and that it was only to be found in the clearest of cases:
[A]buse of process may be established where: (1) the proceedings are oppressive or vexatious; and, (2) violate the fundamental principles of justice underlying the community’s sense of fair play and decency. The concepts of oppressiveness and vexatiousness underline the interest of the accused in a fair trial. But the doctrine evokes as well the public interest in a fair and just trial process and the proper administration of justice.
 In my view, the order dismissing the action as an abuse of process must be set aside. Such orders are only to be granted in the clearest cases and only when allowing the action to proceed would bring the administration of justice into disrepute. The motion judge erred in law in concluding that this was a case of relitigation and that it justified the application of the doctrine of abuse of process.
3. Abuse of Process Contrasted with Issue Estoppel and Res Judicata. Winter v Sherman Estate
In Winter v. Sherman Estate (Ont CA, 2018) the Court of Appeal points out the similarity between abuse of process and issue estoppel, and how abuse of process may be applied where elements of issue estoppel are lacking:
 Further, the appellants too narrowly construe the doctrine of abuse of process. This doctrine is flexible and unencumbered by the specific requirements of res judicata or issue estoppel: Behn v. Moulton Contracting Ltd., 2013 SCC 26 (CanLII),  2 S.C.R. 227, at para 40; Toronto (City) v. C.U.P.E., Local 79, 2003 SCC 63 (CanLII),  3 S.C.R. 77, at para. 42. Where a precondition for issue estoppel has not been met, such as mutuality of parties, courts have turned to the doctrine of abuse of process to preclude re-litigation of the same issue: C.U.P.E., at para. 37. While the doctrine is similar to issue estoppel in that it can bar litigation of legal and factual issues “that are necessarily bound up with the determination of” an issue in the prior proceeding, abuse of process also applies where issues “could have been determined”: Danyluk v. Ainsworth Technologies Inc., 2001 SCC 44 (CanLII),  2 S.C.R. 460, at para. 54; Aba-Alkhail v. University of Ottawa, 2013 ONCA 633 (CanLII), 363 D.L.R. (4th) 470, at para. 13; McQuillan v. Native Inter-Tribal Housing Co-Operative Inc. (1998), 1998 CanLII 6408 (ON CA), 42 O.R. (3d) 46 (C.A.), at paras. 8, 10. As such, the doctrine of abuse of process is broader than res judicata and issue estoppel and applies to bar litigation that, if it proceeded, would “violate such principles as judicial economy, consistency, finality and the integrity of the administration of justice”: C.U.P.E., at para. 37.. Skypower CL 1 LP v Ontario Power Authority
 We agree with the motion judge that the whole evidentiary underpinning of this action is the same as that of the Royal Trust action and that it would be unfair and an abuse of process to allow the appellants to “in effect, re-litigate their case, with a new theory, to see if this one will succeed where previous theories have failed”. Moreover, the doctrine of abuse of process applies to prevent re-litigation of previously decided facts: Intact Insurance Company v. Federated Insurance Company of Canada, 2017 ONCA 73 (CanLII), 134 O.R. (3d) 241, at para. 28, leave to appeal refused,  S.C.C.A. No. 98; R. v. Mahalingan, 2008 SCC 63 (CanLII),  3 S.C.R. 316, at para. 46; C.U.P.E., at para 37. As the motion judge determined, the relief and issues put forward by the appellants in these proceedings “arise from the same relationships and subject matter that have already been dealt with by Perell J. and the Court of Appeal” in the Royal Trust action.
In Skypower CL 1 LP v. Ontario Power Authority (Ont CA, 2015) the same theme was canvassed, that abuse of process can apply to prohibit the raising in future of issues which could have been raised in past proceedings:
 As the motion judge found, the appellants could have raised in the judicial review application—in which they attacked the lawfulness of the Minister’s direction to the OPA, and the resulting changes to the FIT program — the allegation that they were specifically targeted. As this court said in Aba-Alkail v University of Ottawa, 2013 ONCA 633 (CanLII) at para. 12:. Phillion v. Ontario (Attorney General)
…the abuse of process doctrine can apply not only to bar re-litigation of issues that were actually determined in the administrative process, but also to issues that could have been determined (Ontario v. Lipsitz, 2011 ONCA 466 (CanLII) at para. 88). This gives further incentive to raise all issues at the administrative proceeding and to participate "with full vigour". The motion judge was correct in deciding that the appellants’ failure to raise the targeting allegation in the judicial review proceedings was sufficient for the abuse of process doctrine to apply.
 The issue then, is whether the motion judge erred in deciding not to exercise her discretion to permit the action to proceed nevertheless. She found the appellants had a good opportunity to put their position forward in the judicial review proceedings, and the respondents’ refusal to produce certain documents in those proceedings did not result in any unfairness. Her conclusion that “not applying the doctrine of abuse of process in this case would offend the principle of finality and undermine the credibility of the judicial process” is deserving of deference.
 We need not deal with the appellants’ other arguments, as the finding of abuse of process forecloses their equitable as well as their legal claims.
In Phillion v. Ontario (Attorney General) (Ont CA, 2014) the Court of Appeal the court repeats the same theme about the relationship of abuse of process with issue estoppel:
 As it relates to this case, the doctrine has been applied to prevent relitigation when the requirements of issue estoppel cannot be met (as is the case here, because the parties to the two proceedings are not the same), but when “allowing the litigation to proceed would nonetheless violate such principles as judicial economy, consistency, finality and the integrity of the administration of justice”: C.U.P.E., at para. 37. The court emphasized that the focus of the doctrine of abuse of process is less on the parties and more on “the integrity of judicial decision making as a branch of the administration of justice”: C.U.P.E., at para. 43.But at the same time cites this passage from the Supreme Court of Canada:
 In R. v. Mahalingan, 2008 SCC 63 (CanLII), 2008 SCC 63,  3 S.C.R. 316, at para. 42, McLachlin C.J. expressed the view that the doctrine of abuse of process is vague and variable, pointing out that the Supreme Court has said that “successful reliance on the doctrine will be extremely rare”. Importantly for this appeal, she stated further, at para 42, that:
To date, the doctrine has not been much used to protect against relitigation, and indeed there is authority for the proposition that relitigation, without more, simply does not reach the threshold required for a finding of abuse of process. [Citation omitted.]
4. Abuse of Process in Relation to Other Doctrine. Apotex Inc. v. Schering Corporation
In Apotex Inc. v. Schering Corporation (Ont CA, 2018) the Court of Appeal applies it's discretion not to apply the equitable doctrine of issue estoppel if it would an injustice in the case, and in doing so identifies the doctrines of issue estoppel and collateral attack as sub-categories of the larger doctrine of abuse of process:
 I would note, at the outset, that the scope of the “special circumstances” exception to issue estoppel constitutes a question of law. The standard of review is thus one of correctness: Housen v. Nikolaisen, 2002 SCC 33 (CanLII),  2 S.C.R. 235, at para. 8.
 The requirements of, and purpose behind, the doctrine of res judicata were thoroughly canvassed in Danyluk v. Ainsworth Technologies Inc., 2001 SCC 44 (CanLII),  2 S.C.R. 460. In that decision, Binnie J. reviewed the historical development of the doctrine and its component parts: cause of action estoppel and issue estoppel. He also reviewed the development of the doctrine of collateral attack.
 As set out in Danyluk at para. 25, the preconditions to the operation of issue estoppel are: (i) that the same question has been decided; (ii) that the judicial decision which is said to create the estoppel was final; and, (iii) that the parties to the judicial decision or their privies were the same persons as the parties to the proceedings in which the estoppel is raised or their privies. It is clear that those three preconditions are met in this case.
 However, Binnie J. went on in Danyluk to point out that the court retained a discretion not to apply the doctrine where to do so would work an injustice. More specifically, Binnie J. adopted the observation in British Columbia (Minister of Forests) v. Bugbusters Pest Management Inc. (1998), 1998 CanLII 6467 (BC CA), 159 D.L.R. (4th) 50 (B.C.C.A.) where Finch J.A. said, at para. 32:
It must always be remembered that although the three requirements for issue estoppel must be satisfied before it can apply, the fact that they may be satisfied does not automatically give rise to its application. Issue estoppel is an equitable doctrine, and as can be seen from the cases, is closely related to abuse of process. The doctrine of issue estoppel is designed as an implement of justice, and a protection against injustice. It inevitably calls upon the exercise of a judicial discretion to achieve fairness according to the circumstances of each case. Binnie J. added, at para. 67:
The objective is to ensure that the operation of issue estoppel promotes the orderly administration of justice but not at the cost of real injustice in the particular case. Finally, Binnie J. concluded with a statement of what he said was the most important factor in deciding whether issue estoppel ought to be applied in any given case. He said, at para. 80:
As a final and most important factor, the Court should stand back and, taking into account the entirety of the circumstances, consider whether application of issue estoppel in the particular case would work an injustice. The exercise of the discretion to apply issue estoppel was also the subject of the decision of this court in Minott v. O'Shanter Development Co. (1999), 1999 CanLII 3686 (ON CA), 42 O.R. (3d) 321 (C.A.). Of particular importance, for the purposes of this case, is the observation of Laskin J.A. at para. 51 where he said:
If the decision of a court on a point of law in an earlier proceeding is shown to be wrong by a later judicial decision, issue estoppel will not prevent relitigating that issue in subsequent proceedings. It would be unfair to do otherwise.....
 For the reasons set out above, the appellants’ proposed amendments are also not barred by the doctrine of collateral attack. In Toronto (City) v. C.U.P.E., Local 79, 2003 SCC 63 (CanLII),  3 S.C.R. 77, the Supreme Court of Canada described issue estoppel and collateral attack as “particular applications of a broader doctrine of abuse of process” [italics added] (at para. 22). Though not entirely interchangeable, the Supreme Court went on to hold the following, at para. 53:
The discretionary factors that apply to prevent the doctrine of issue estoppel from operating in an unjust or unfair way are equally available to prevent the doctrine of abuse of process from achieving a similar undesirable result.As the application of collateral attack in this case would work the same injustice as issue estoppel, it should not be applied to block the proposed pleadings.
5. Abuse of Process and the Rules of Civil ProcedureThe doctrine of abuse of process, while ill-defined, has seen itself taken up wholeheartedly by the court rules, here the Rules of Civil Procedure, the main rules of the workhorse Superior Court of Justice. It finds itself in such company as the 'doctrine' of frivolous and vexatious.
Here is a typical such reference [others are located at R2.1.01, R2.1.03, R21.01(3), R25.11 and 37.16]:
2.1.01 (1) The court may, on its own initiative, stay or dismiss a proceeding if the proceeding appears on its face to be frivolous or vexatious or otherwise an abuse of the process of the court.