Criminal procedure is an integral but distinct part of criminal law in Canada. It is distinct from the substance of criminal law in that it does not define the type of conduct that constitutes a criminal offence or establishes punishment, but rather determines by whom and in what circumstances prosecutions against accused offenders may be initiated, conducted, terminated and appealed. Criminal procedure is a set of rules according to which the substantive law is administered. The principal objective of criminal law procedure is to ensure a fair and just process in the determination of guilt or innocence. This determination is made in accord with those principles that Canadians have accepted as reflecting the proper balance between the value of protection of society and the value of individual freedom (see Law and Society).

Criminal procedure commences long before an accused person appears in court, as detailed laws cover how police may investigate a crime (see Criminal Investigation). For example, there are many procedural rules in the Criminal Code or in the common law that define how and when police may interrogate witnesses or suspects, search persons and places, arrest suspects, seize evidence, and use telephone wiretaps. Criminal procedure then sets out the rules as to how a charge is laid, when accused persons will obtain bail, and in what court they will eventually have their trial. The actual court process is set in motion by the swearing of an Information (popularly known as a charge) before a justice of the peace or magistrate (provincial court judge). An Information is an allegation by a citizen (usually a police officer) that reasonable and probable grounds exist to believe another person (the accused) has committed a crime.

All offences in Canada may be classified as indictable (the more serious) or summary conviction (the less serious). Some offences may, at the discretion of the Crown, be prosecuted either by indictment or by summary conviction. The trial of summary conviction offences is either before a magistrate or a justice of the peace, and generally they carry a maximum punishment of $2000 or 6 months in prison. Summary conviction proceedings generally have a limitation period of 6 months from the date of the offence.

Procedure with respect to indictable offences is more complicated and varies from province to province. Depending upon the type of indictable offence, the Criminal Code will determine whether the trial can be heard by a magistrate, a high-court judge (County Court, District Court, Supreme Court or Queen's Bench judges appointed by the federal government), or by a court composed of a high court sitting with a jury. Generally, when an accused is going to have a trial by a high-court judge or by a court composed of a judge and jury, he has the right to a preliminary hearing. There are several procedural provisions in the Criminal Code that deal with how the preliminary hearing should be conducted and what rights the accused has at this stage of the criminal prosecution. The preliminary hearing is held by a magistrate and the crown prosecutor presents the witnesses that he will rely upon at the trial. The accused through his counsel is allowed to cross-examine these witnesses. The public is allowed to attend, but often the press are not able to report the evidence heard. The issue at the preliminary hearing is not to determine innocence or guilt but to determine whether there is sufficient evidence to justify a trial. If it is decided sufficient evidence exists, the accused will be ordered to stand trial in the higher court by the magistrate.

There is no specific time limitation regarding when an accused must be charged with an indictable offence, although the Canadian Charter of Rights and Freedoms requires that, once charged, the accused be tried within a reasonable time. The maximum punishment for each indictable offence is set out in the Criminal Code and varies from offence to offence.

Whether an accused is charged with a summary conviction offence or an indictable offence, he is eventually called upon to state in open court whether he pleads guilty or not guilty. If the plea is not guilty, the case will proceed to trial; if guilty, then a sentencing will take place before the judge who received the plea. There are several procedural rules as to how guilty pleas may be entered and how a judge may sentence an accused. In all criminal cases, both the accused and the Crown may have statutory rights of appeal against the determination of guilt or innocence, as well as sentence. Once again, there are many procedural rules governing appeals.

There are different theories concerning the best method of achieving a balance between the control of crime and the protection of individual rights. In Canada, England and the US, an adversarial or accusatorial system is used, in contrast to the inquisitorial system practised in France and other European countries. Canadian procedural rules are therefore designed to support the adversarial system in which the proceeding is a dispute between the state or Crown and the defendant or accused. As has been indicated above, the parties appear before an independent arbitrator, either a judge or jury, who must determine whether the accused is guilty or not guilty. Both parties are responsible for gathering and presenting evidence. The arbitrator is expected to play a relatively passive role, maintaining an impression of independence and impartiality, and ensuring that the rules of procedure are observed. In contrast, the inquisitorial system is a judicial inquiry. The responsibility for investigating and bringing out the facts rests upon the decision maker. The parties' roles are restricted to ensuring that their interests are properly represented during the trial.

The adversarial system and the procedural rules which comprise that system unquestionably favour the accused to a greater degree than the inquisitorial system. The Crown generally has the burden of adducing evidence to prove the guilt of the accused, who is almost always entitled to a presumption of innocence until the Crown has proven otherwise beyond a reasonable doubt. The accused is not required to give evidence and the court must acquit him if the Crown has not proven its case. If the accused elects not to give evidence or call witnesses, he (through his counsel) is still actively involved in the trial through cross-examinations of crown witnesses. This is very different from the inquisitorial system in which the accused is generally subjected, without election on his part, to extensive questioning but is otherwise inactive in the process.

Nevertheless, certain principles are common to both systems, including the requirements that trials be public, that determinations be based on evidence presented in open court, and that the accused is presumed innocent until proven guilty. However, even though both systems share these fundamental principles, there are differences in the manner in which they are applied.

The Constitution Act of 1867 gave the federal government jurisdiction to legislate with respect to "the criminal law, except the constitution of Courts of criminal jurisdiction, but including the procedure in criminal matters." Pursuant to this authority, Parliament has incorporated most Canadian procedural rules in the Criminal Code. Also, related statutes such as the Narcotic Control Act include their own specific procedures. One must remember that much criminal procedure is established by the Courts, as the various legislative provisions dealing with procedure often require interpretation.

A very important development in Canadian criminal procedure (as in most, if not all, areas of criminal law) is the inclusion of the Canadian Charter of Rights and Freedoms into the Constitution Act of 1982. Although the Charter does not set out any procedural rules, it does provide many of the principles that procedural rules must follow. Legislative procedures, such as the reverse onus requirement (in which the accused must prove his innocence) under the "possession for the purpose of trafficking" offence found in the Narcotic Control Act, have been struck down as contrary to the Charter.

Judicial interpretation of procedural rules has also been affected by the Charter. For instance, the police now have to be much more careful, when questioning suspects, to ensure that they are aware that they have the right to consult with a lawyer without delay as is guaranteed by s10(B) of the Charter. If the police do not allow an accused to exercise this right, then there is an excellent chance that any confession or other evidence subsequently obtained will be declared inadmissable. Formerly, a violation of this nature did not generally result in the exclusion of evidence. The courts have also found that the Charter requires the Crown, before trial, to fully disclose to the accused all information or evidence it has in its possession which may bear in any way on the issue of guilt or innocence. If there has not been full disclosure the accused is entitled to adjourn a trial or, if already convicted, to have the conviction struck and a new trial ordered.