The origins of the Jury system are up for debate; however it may be said to be founded in the Frankish inquest, and transplanted into England by the Norman Kings.
It was meant to replace rather dubious and barbaric methods of trial, such as Trial by Ordeal, or Trial by Combat.
Today, the jury does not know beforehand the facts of the case or the parties. This is in contrast to the way it was in the 12th century. Initially the Shire Reeve (Sheriff) would swear 4 knights, who would in turn selected 12 good knights who knew the litigant and the issues, and swore upon Oath to determine the issues.
In the US, this jury system was also created to prevent abuses from Royal interference and to ensure that it was in fact, the people, and not the government, that decided the fates of their fellow citizens. The US also has different types of juries, including, petit and grand jury.
In a typical criminal case, potential jurors are summoned by the Sheriff's Office and instructed to appear before the judge and lawyers on a certain day. These jurors will be seated behind the bar in the observers' seats. It is here that the lawyers begin the process of selecting the jury.
In the US, this examination and selection process includes a dialogue between the potential jurors and lawyers, in what is called a voir dire (French for "to speak the truth").
In comparison to the US process, the Canadian voir dire is curtailed significantly, with little dialogue between the lawyers and jury pool. The voir dire is a truth-seeking process where the lawyers try to cleanse the jury pool from any unfair prejudice or bias that may jeopardize the fairness of the proceedings.
This process of removal is called "challenging" the juror. There are two types of challenges:
1) challenges for cause; and
2) peremptory challenges.
The first type of challenge is where it is believed that the juror cannot sit as an impartial decision maker.
The second category - principled on the requirements of a fair trial - is reserved for the lawyers to strike a potential juror for almost whatever reason. However, this is not an absolute and unfettered power.
For example, in the US, a Defendant may raise what is called a Batson claim (named after the case in which the principal was enunciated) where there is an allegation that the prosecutor has stricken all the jurors of the same race as the defendant on the basis of race alone.
Jurors may also be excused by the judge for other reasons, such as undue burdens that the trial will cause on the juror, or other human frailties. It is important to know that if one is dismissed from jury duty, it is not necessarily a reflection on one's character, or disposition. It simply means that that person was not suitable, for whatever reason, on that day, for that specific trial.
Within a trial by jury, there is an important element called "Jury Nullification"
In Robert Latimer's case, wherein he was convicted of second degree murder following death of his severely disabled daughter by a jury of his peers, he later appealed to the Supreme Court of Canada on the question, inter alia of:
Did the trial judge render the appellant's trial unfair because of trial procedures that might have lessened the chance of jury nullification?
And this is what the Supreme Court of Canada stated on Jury Nullification in the Latimer Case vs. the Majesty the Queen, 2001, SCC 1.File No.: 26980:
(3) Jury Nullification
57 The term "jury nullification" refers to that rare situation where a jury knowingly chooses not to apply the law and acquits a defendant regardless of the strength of the evidence against him. Jury nullification is an unusual concept within the criminal law, since it effectively acknowledges that it may occur that the jury elects in the rarest of cases not to apply the law. The explanation seems to be that on some occasions, oppression will result either from a harsh law or from a harsh application of a law.
58 This Court has referred to the jury's power to nullify as "the citizen's ultimate protection against oppressive laws and the oppressive enforcement of the law" and it has characterized the jury nullification power as a "safety valve" for exceptional cases: R. v. Morgentaler,  1 S.C.R. 30 ("Morgentaler (1988)"), at pp. 78-79. At the same time, however, Dickson C.J. warned that "recognizing this reality [that a jury may nullify] is a far cry from suggesting that counsel may encourage a jury to ignore a law they do not support or tell a jury that it has a right to do so" (emphasis in original).
59 The appellant effectively makes two arguments, one specific and one general. His specific argument is that the trial judge interfered with the jury's ability to nullify by implying that the jury could offer input on sentencing. His general argument is that an accused person must have some right to a jury that is more likely to nullify. We will consider each argument in turn.
60 The appellant submits that his trial was unfair because of what he characterizes as the trial judge's misleading answer to the jury's inquiry as to whether it could offer input on sentencing. In the course of its deliberations, the jury sent the trial judge a note inquiring, in part, whether it could offer any input into sentencing. The trial judge was clear in reply that the jury was not to concern itself with the matter of penalty, but should focus solely on the question of guilt. The trial judge added, "it may be that later on, once you have reached a verdict, you -- we will have some discussions about that [penalty]".
61 The appellant argues that the trial judge ought to have clarified his "misleading" suggestion that the jury could influence the penalty by explicitly telling the jury of the mandatory minimum sentence of life without parole for 10 years.
65 An accused is entitled to a fair trial, including the presumption of innocence, the duty of the Crown to prove guilt beyond a reasonable doubt, and the ability to make full answer and defence. The accused is not entitled to a trial that increases the possibility of jury nullification. If the trial of the accused has not been unfair and no miscarriage of justice has occurred, the accused cannot succeed on an argument that due to some departure from the norm by the trial judge, his chances of jury nullification are lessened. This point is treated in further detail below.
68 The appellant's second argument is a broad one, that the accused person has some right to jury nullification. How could there be any such "right"? As a matter of logic and principle, the law cannot encourage jury nullification. When it occurs, it may be appropriate to acknowledge that occurrence. But, to echo the words of Morgentaler (1988), saying that jury nullification may occur is distant from deliberately allowing the defence to argue it before a jury or letting a judge raise the possibility of nullification in his or her instructions to the jury.
69 The appellant concedes as much, but advances some right, on the part of the accused person, to a jury whose power to nullify is not undermined. He suggests the right to a fair trial under s. 7 of the Charter encompasses this entitlement. The appellant submits that there is a jury power to nullify, and it would be unconstitutional to undermine that power.
70 We reject that proposition. The appellant cannot legitimately rely on a broad right to jury nullification. In this case, the trial did not become unfair simply because the trial judge undermined the jury's de facto power to nullify. In most if not all cases, jury nullification will not be a valid factor in analyzing trial fairness for the accused. Guarding against jury nullification is a desirable and legitimate exercise for a trial judge; in fact a judge is required to take steps to ensure that the jury will apply the law properly. See R. v. Shipley (1784), 4 Dougl. 73, 99 E.R. 774 (K.B.), at p. 824, cited with approval by Dickson C.J. in Morgentaler (1988), at p. 78. Steps taken by a trial judge to guard against jury nullification should not, on that basis alone, prejudice the accused person.
It is clear that the Supreme Court of Canada, mainly Madam Chief Justice Beverly McLachlin, has managed to castrate the jurors' of their right to Jury Nullification, or in the very least for the Jurors' to exercise their power.
This is to say that today those being tried before a jury cannot ever receive a fair trial, just like Robert Latimer who is serving time in jail, when he should have been acquited.