My state allows people who have been charged with crimes, but not tried or convicted, to be released from jail by posting cash bail, by purchasing a bail bond, or even on a "personal recognizance" bond. However, I've heard that judges usually impose conditions on release, like ordering a person to attend anger management classes or abstain from excessive use of alcohol. How can the judge impose these conditions when a person is still presumed innocent?
The 8th Amendment to the U.S. Constitution states that excessive bail shall not be required. This means that people charged with crimes normally have an opportunity to pay their way out of jail while charges are pending. People who are especially likely to return to court as ordered and who do not pose a threat to personal safety may even leave jail without paying a cent, by posting a "personal recognizance bond," also known as "release OR" or being let out on one's "own recognizance."
But whether arrested persons buy a bail bond or are released OR, judges can and almost always do impose conditions on their release. Though arrested persons are presumed innocent, the government has a right to keep them in jail until their guilt or innocence is determined -- so long as the government does not require excessive bail. And when arrested persons are released, judges have the right to protect the community by imposing reasonable conditions on their release.
What's reasonable? Some conditions are common to all pretrial releases, such as conditions that a person obey all laws, show up in court as ordered, and not leave the jurisdiction without permission. Other conditions are related to the specific charge in an individual case. For example, a person arrested for domestic violence may be ordered to attend anger management classes while charges are pending. Also, a judge might require a defendant charged with drug possession to attend Narcotics Anonymous meetings.
The more serious the pending charges, the more restrictive the conditions tend to be. A defendant who fails to comply with the conditions of release may find him or herself returned to jail -- or at the very least facing an angry judge (which is not a great strategic move). That's a pretty big incentive not to be tardy to or absent from a court date! To learn more about bail and conditions of bail, see Nolo's article Bail: Getting Out of Jail After an Arrest.