Mitigation is not likely to be of great concern to rehabilitationists, except as they observe proportionality constraints. Further, mitigation is not likely to be a central issue for incapacitative theorists unless it affects predictions of the offender's future conduct. In just deserts and deterrence theories, however, proportionality and mitigation are especially important. As part of the process of assessing offense seriousness, identifying factors that render a certain crime more or less serious may be seen as a specific aspect of the general task of determining the relative seriousness of different crime types. Offense-related mitigating factors are explored, particularly in terms of whether sentences should be mitigated based on acts of heroism by the offender, collateral pains suffered by the offender, employment record of the offender, or social deprivation in the offender's background. The author concludes that good arguments exist within just deserts theory for mitigation based on significant social disadvantage and deprived upbringing but that support for other mitigating factors such as acts of heroism, collateral pains, and employment record can only be found outside principles of proportionality. 25 notes