In some jurisdictions, the term probation applies only to community sentences (alternatives to incarceration), such as suspended sentences. In others, probation also includes supervision of those conditionally released from prison on parole.
An offender on probation is ordered to follow certain conditions set forth by the court, often under the supervision of a probation officer. During the period of probation an offender faces the threat of being incarcerated if found breaking the rules set by the court or probation officer.
Offenders are ordinarily required to refrain from possession of firearms, and may be ordered to remain employed or participate in an educational program, abide to a curfew, live at a directed place, obey the orders of the probation officer, or not leave the jurisdiction. The probationer might be ordered as well to refrain from contact with the victims (such as a former partner in a domestic violence case), with potential victims of similar crimes (such as minors, if the instant offense involves child sexual abuse), or with known criminals, particularly co-defendants. Additionally, the restrictions can include a ban on possession or use of alcoholic beverages, even if alcohol was not involved in the original criminal charges. Offenders on probation might be fitted with an electronic tag (or monitor), which signals their movement to officials. Also, offenders have been ordered to submit to repeat alcohol/drug testing or to participate in alcohol/drug or psychological treatment, or to perform community service work. Some courts permit defendants of limited means to perform community service in order to pay off their probation fines.
The concept of probation, from the Latin, probatio, "testing," has historical roots in the practice of judicial reprieve. In English common law, prior to the advent of democratic rule, the courts could temporarily suspend the execution of a sentence to allow a criminal defendant to appeal to the monarch for a pardon.
Probation first developed in the United States when John Augustus, a Boston cobbler, persuaded a judge in the Boston Police Court in 1841 to give him custody of a convicted offender, a "drunkard," for a brief period and then helped the man to appear rehabilitated by the time of sentencing. Even earlier, the practice of suspending a sentence was used as early as 1830 in Boston, Massachusetts, and became widespread in U.S. courts, although there was no statutory provision for such a practice. At first, judges, most notably Peter Oxenbridge Thatcher of Boston, used "release on recognizance" or bail and simply refrained from taking any further action. In 1878 the mayor of Boston had hired a former police officer, the ironically named "Captain Savage," to become what many recognize as the first official probation officer. By the mid-19th century, however, many Federal Courts were using a judicial reprieve to suspend sentence, and this posed a legal question. In 1916, the United States Supreme Court, in the Killets Decision, held that a Federal Judge (Killets) was without power to suspend a sentence indefinitely. This decision led to the passing of the National Probation Act of 1925, thereby, allowing courts to suspend the imposition of incarceration and place an offender on probation. Probation developed from the efforts of a philanthropist, John Augustus, who looked for ways to rehabilitate the behavior of criminals.
Massachusetts developed the first statewide probation system in 1878, and by 1920, 21 other states had followed suit. With the passage of the National Probation Act on March 5, 1925, signed by President Calvin Coolidge, the U.S. Federal Probation Service was established. On the state level, pursuant to the Crime Control and Consent Act of 1936, a group of states entered into an agreement wherein they would supervise probationers and parolees who reside in each other's jurisdictions on each other's behalf. Known as the Interstate Compact For the Supervision of Parolees and Probationers, this agreement was originally signed by 25 states in 1937. By 1951, all the states in the United States of America had a working probation system and ratified the Interstate Compact Agreement. In 1959, the new states of Alaska and Hawaii, the Commonwealth of Puerto Rico, and the territories of the Virgin Islands, Guam, and American Samoa ratified the act as well.
In the United States, most probation agencies have armed officers. In 39 states, territories and federal probation, such arming is either mandated or optional. Arming is allowed in an increasing number of jurisdictions.
Probation officers are peace officers who possess limited police powers.
Intensive probation, home detention, GPS monitoring, Computer Management These are highly intrusive forms of probation in which the offender is very closely monitored. It is common for violent criminals, higher-ranking gang members, habitual offenders, and sex offenders to be supervised at this level. Some jurisdictions require offenders under such supervision to waive their constitutional rights under the Fourth Amendment regarding search and seizure, and such probationers may be subject to unannounced home or workplace visits, surveillance, and the use of electronic monitoring or satellite tracking. Under terms of this kind of probation, a client may not change their living address and must stay at the address that is known to probation. GPS monitoring and home detention are common in juvenile cases, even if the underlying delinquency is minor. Some types of supervision may entail installing some form of monitoring software and/or conducting computer searches to ascertain what an offender is doing online. Cybercrime specialist in corrections, Art Bowker, noted “This is an area more and more community corrections officers are going to have to get up to speed on, learning how to enforce conditions that restrict and/or monitor cyber offenders' computer and internet use.” Bowker, also observed "The use of social media is taking off in the field of community corrections." 
Standard supervision Offenders under standard supervision are generally required to report to an officer, most commonly between biweekly and quarterly, and are subject to any other conditions as may have been ordered, such as alcohol/drug treatment, community service, and so on.
Unsupervised probation does not involve direct supervision by an officer or probation department. The probationer is expected to complete any conditions of the order with no involvement of a probation officer, and perhaps within a period shorter than that of the sentence itself. For example, given one year of unsupervised probation, a probationer might be required to have completed community service, paid court costs or fines, etc., within the first six months. For the remaining six months, he or she may be required merely to refrain from unlawful behavior. Probationers are allowed to go to their workplace, educational institution, or place of worship. Such probationers may be asked to meet with an officer at the onset or near the end of the probationary period, or not at all. If terms are not completed, an officer may file a petition to revoke probation.
Informal supervision is supervised or unsupervised probation without having been convicted of the offense. As with other forms of probation, search clauses or drug testing may be included. At the end of the informal period, the case is dismissed. This is usually offered as part of a plea bargain or pre-trial diversion, and may requires the supervisee to waive Fourth Amendment rights for the duration. Informal probation can also require the supervisee to enter a plea of "Guilty", pending the completion of the terms set forth in the agreement, at which time the charge is typically dismissed.
Shock probation is a program that gives a sentencing judge the power to reconsider an original jail sentence. The judge may recall the inmate from jail and put him or her on probation within the community instead. The courts have a theory that a short term in jail may “shock” a criminal into changing their behavior. Shock probation can be used only between a specific period of 30–120 days after the original sentence, and is not available in all states.
Community corrections officials are the main factors that help decide whether a criminal is granted probation or not. They are the ones who determine whether the offender is a serious risk to public safety. These officials are also the ones who make recommendations to the court on what action to take. The correction officials first go through an investigations process during the pretrial period. They assess the offenders background and history to determine if he or she can be released safely back into the community. The officers then write a report on the offender. This is an extremely important piece of information that the courts use to determine if the offender shall be put on probation instead of going to jail. After the offender is found guilty, the probation officer puts together a pre-sentence investigation report (PSI). Courts base their sentencing on it. Finally, courts make their decision whether to imprison the convict or to let him or her off on probation. If a court decides to grant a person probation, it must then determine how to impose the sentence based on the seriousness of the crime, recidivism, circumstances of the convict, and the recommendations from the corrections officials.
A probation officer may imprison a probationer and petition the court for a violation of probation. The court will request that the defendant appear at a show cause hearing at which the prosecutor must demonstrate by a preponderance of the evidence that the defendant committed a probation violation. If the defendant pleads guilty to a probation violation, or is found guilty of a probation violation after the hearing, the officer or prosecutor may request that additional conditions of probation be imposed, that the duration be extended, or that a period of incarceration be ordered, possibly followed by a return to probation. There is no law that specifies when probation violation proceedings must be commenced, although probation violation proceedings are near certain following the defendant's conviction of a subsequent offense, or failure to report to the probation officer as ordered.
If a violation is found, the severity of the penalties may depend upon the facts of the original offense, the facts of the violation, and the probationer's criminal history. For example, if an offender is on probation for a gang-related offense, subsequent "association with known criminals" may be viewed as a more serious violation than if the person were on probation for driving a car with a suspended license; the reverse may be true if the initial offense were for driving under the influence. Similarly, penalties for violation may be greater if a subsequent offense is of greater severity (such as a felony, following a misdemeanor), or if the original offense and subsequent offense are of the same type (such as a battery following an assault, or retail theft following retail theft).
When a probation violation is extremely severe, or after multiple lesser violations, a probation revocation hearing could be scheduled. A judge at the hearing will consider reports from the probation officer, and if probation is revoked, the probationer will often be incarcerated in jail or prison. However, the term of incarceration might be reduced from the original potential sentence for the alleged crime(s). It is possible that an innocent defendant would choose to accept a deferred sentence rather than incur the risk of going to trial. In such a case, a probation revocation can result in conviction of the original criminal charges and a permanent record of conviction.