Three areas in which the nature of the prosecutor's dual role can be illustrated are in the grand jury, in pretrial discovery, and at the trial itself. The American Bar Association has adopted a standard for grand jury practice which provides that no prosecutor shall knowingly fail to disclose exculpatory evidence. However, prosecutors neither have to develop such evidence nor are limited in exercising their judgment to decide what evidence to present so long as the evidence is not calculated to inflame or improperly influence the jurors. In the discovery process tension exists between the defendant's interest in full disclosure and the government attorney's interest in effective trial advocacy. Prosecutors must ensure that all relevant law enforcement agencies have produced their reports and accumulated evidentiary materials, and they should be prepared to respond to defense attempts to identify other sources of discoverable documents. One major area in which the adversary struggle over discovery goes on unabated is in defense attempts to secure the names of government witnesses. A legitimate argument can be made that the defense cannot adequately prepare without access to them. However, witnesses and victims are vulnerable to attempts to influence their testimony, and the risk that the trial process might be perverted may far outweigh the interest of the defense. Thus, an absolute obligation to disclose would not be appropriate. At trial the prosecutor and the defense move into the public stage. Prosecutors must be constantly alert that they do not come close to the bounds of propriety; they are constantly at risk of being perceived to be misusing their power. Thus, prosecutors who deal forthrightly and flexibly with witnesses, defendants, and defense counsel serve both systemic values and their goals as advocates. However, compliance with constitutional, statutory, and ethical standards is not enough. Prosecutors must act within the full spirit of their role. Footnotes are included.