The difference between probation and parole is that probation is typically used in lieu of incarceration and places an offender under court ordered supervision by a probation agency. Parole is used to conditionally release an offender from incarceration to complete his remaining sentence in the community.
An offender on probation is often given the opportunity to prove to the court that he can rehabilitate himself. In many cases, the sentencing judge may give the offender probation and no prison sentence. In others, the judge may find the offender guilty but not require him to serve the sentence provided he abides by the conditions imposed by the court, such as maintaining a curfew, participating in rehabilitation programs, periodic drug testing and payment of fines and court costs. If he violates the conditions he can be sent to prison to complete his sentence for the original crime, and potentially serve additional prison time for a probation violation. Ultimately, the judge has the power to modify the conditions of probation.
Parole occurs after an offender has served some time in incarceration. The offender is required to report to a parole officer, who lays out a framework of rules and expectations that the offender must follow and tracks his progress. Parole also subjects the offender to a wide array of conditions, which if violated, can result in the offender being sent back to prison to finish the remainder of his sentence. The parole board is tasked with establishing the condition of parole and any accompanying penalties for violation of conditions.