Section 606(1) describes the pleas available to an accused who is called upon to plead. The section makes it clear that, apart from the general pleas of guilty and not guilty and the special pleas authorized by Part XX, no other pleas are available. Thus, a formal plea of nolo contendere, literally "I am unwilling to contest", is not available under our procedural law.
 A plea of guilty is a formal admission of guilt and constitutes a waiver, not only of an accused's right to require the Crown to prove its case by admissible evidence beyond a reasonable doubt, but also of various related procedural safeguards, including those constitutionally protected: R. v. T. (R.) (1992), 10 O.R. (3d) 514 (C.A.), at p. 519; Korponay v. Canada (Attorney General),  1 S.C.R. 41, at p. 49.
 A plea of guilty must be voluntary, unequivocal, and informed. A voluntaryplea is a conscious, volitional decision by an accused to plead guilty for reasons that he or she considers appropriate: T. (R.), at p. 520. An informed plea is a plea entered by an accused who is aware of the nature of the allegations made against him or her, the effect of his or her plea, and the consequences of that plea: T. (R.), at p. 519; R. v. Lyons,  2 S.C.R. 309, at p. 371-372.
 On the other hand, an accused who pleads not guilty puts the Crown on notice that she or he requires the Crown to prove every essential element of the offence charged, by evidence that is relevant, material, and admissible, to the exclusion of reasonable doubt, and in accordance with applicable procedural safeguards: R. v. G. (D.M.), 2011 ONCA 343, 275 C.C.C. (3d) 295, at para. 52. The manner in which the Crown proves its case is for the Crown to decide, subject to the authority of the trial judge to determine issues of relevance, materiality, and admissibility of the evidence, and to ensure that the proceedings comply with any applicable procedural requirements and constitutional standards.
 Among the methods of proof available to the Crown are admissions of fact governed by s. 655 of the Criminal Code. Under that provision, it is for the Crown, not the defence, to state the fact or facts that it alleges against the accused and of which it seeks admission. The accused may choose to admit the facts, or decline to do so. Admissions require action by two parties, one who makes the allegation and the other who admits it. Once the admission is made, no other proof of the facts admitted need be offered: Castellani v. The Queen,  S.C.R. 310, at pp. 315-317.
 Sometimes, formal admissions of fact under s. 655 may constitute the entirety of the Crown's case. For example, in R. v. Cooper,  1 S.C.R. 860, the Crown's case-in-chief consisted of an agreed statement of facts. The Supreme Court of Canada described the procedure as unusual, but did not suggest that it was legally impermissible or procedurally flawed. A similar procedure is followed by some courts in one-stage trials on the issue of criminal responsibility.