This volume explores an under-researched yet fascinating domain in the field of criminal sentencing: the circumstances that may justify imposition of a harsher or more lenient sentence. At sentencing, courts must weigh a wide range of offence and offender-related factors in order to determine the severity of the sentence. Some factors influence the sentence by affecting the seriousness of the crime, others because they reflect a higher or lower level of culpability on the part of the offender. Mitigating and aggravating factors are often taken for granted by members of the public (and possibly some legal professionals) – we all have intuitions about whether factor X should result in a more lenient or a harsher sentence. Certainly, for many factors the relevance is obvious: committing an assault against someone while disparaging their ethnicity or religious beliefs obviously makes the assault more serious; there is an additional element of harm (contained in the affront to the victim’s identity). Similarly, if, immediately after committing the crime the offender assists the victim, apologizes for his conduct and makes amends, this justifies a more lenient sentence. But many problematic circumstances exist.