Under the mandates of the U.S. Constitution, a criminal prosecutor engages in a balancing act under conflicting obligations. On the one hand, he/she must advocate for his/her client, the citizenry of the community from which he/she is appointed or elected; and on the other hand, he/she must act to protect the criminal defendant's constitutional rights and fairly participate in the search for justice. Because prosecutors have the sole power to initiate judicial action in a criminal case, they are the most powerful players within the criminal justice system. Because there is little independent control over a prosecutor's discretion in charging or not charging a suspect, the prosecutor's ethical and legal commitment to justice is critical. Prosecutors have the ethical and legal obligation to ensure that innocent persons are not unfairly charged and that the evidence against a suspect is, in the judgment of the prosecutor, sufficient to support a specific charge. Not only does the prosecutor have critical ethical and legal decisions to make in the pretrial stage -- which includes the investigation, arrest, decision to prosecute, charging, and arraignment -- but he/she also must fulfill ethical duties in the finding of guilt or innocence either by trial or plea negotiation, as well as in the posttrial phase, which includes sentencing, appeals, and parole. This chapter examines prosecutorial ethical responsibilities in the performance of duties at each of these stages of case processing. 13 notes and 5 references