Imposing a sentence (the punishment given to an offender) can be one of the most exacting tasks undertaken by a judge. By law sentences must reflect a number of considerations, some of which may be in conflict.  Some of the most important considerations are:
- the seriousness of the offending
- the interests of the victim
- consistency with sentences imposed for similar offending
- the personal circumstances of the offender
A former Chief Justice of New South Wales put it this way: 
The … core of the sentencing task is a process of balancing overlapping, contradictory and incommensurable objectives. The requirements of deterrence, rehabilitation, denunciation, punishment and restorative justice, do not generally point in the same direction. Specifically, the requirements of justice, in the sense of just deserts, and of mercy, often conflict. Yet we live in a society which values both justice and mercy.
The sentencing of offenders convicted of imprisonable offences is generally postponed following conviction, to enable the sentencing judge to obtain reports and written submissions to inform these.
As a rule, the judge directs the preparation of a pre-sentence report about the offender's personal circumstances. The police are required by law to obtain an impact statement from the victims and sometimes their families. Victims may ask to be allowed to read these statements in Court, and certain victims, such as victims of serious assaults or sexual crimes are entitled to read their statements as of right if they wish, unless a judge considers it inappropriate to do so.  Lawyers representing the offender and the prosecution have the opportunity to prepare submissions relating to sentences previously imposed in similar cases and as to the appropriate sentence.
Until Parliament passed this Act the purposes and principles of sentencing were mostly based on earlier cases.
The Sentencing Act defines the purposes of sentencing, but does not require that any particular purpose must be given greater weight than others. The purposes include: 
- holding the offender accountable
- promoting in the offender a sense of responsibility
- providing for the interests of the victim (including by ordering reparation for harm done)
- denunciation of the offender's conduct
- deterrence of both the offender and other persons
- protection of the community and
- assisting in the offender's rehabilitation and reintegration back into the community
The Act then identifies principles which judges must take into account. These include: 
- the gravity of the offending
- the culpability (blameworthiness) of the offender
- the maximum penalty prescribed for the offence
- the desirability of consistency of sentences for similar offending
- the personal circumstances of the offender including personal characteristics which may make a sentence disproportionately severe upon that particular person, and
- whether any restorative justice agreements or terms have been reached
New Zealand is a leader internationally in the area of restorative justice. Typically this involves face-to-face contact between the offender and the victim. This process may result in agreement as to how the offender may make amends for his offence, whether by apology, compensation, performance of work or services or any other response which is acceptable to the victim. When, subsequently, the offender is sentenced, the sentencing judge must take account of the restorative justice outcomes when deciding upon the appropriate sentence of the court and may reduce the sentence to reflect the fact that the offender has accepted responsibility for his or her actions.
Judges routinely order a pre-sentence report where an offender pleads guilty to, or is convicted of an offence punishable by imprisonment. Pre-sentence reports are prepared by probation officers, who also supervise offenders living in the community after receiving community-based sentences or after their release from prison.
Pre-sentence reports contain information about:
- The offender's personal background and family (whanau) circumstances
- The lifestyle and other factors which are considered to have contributed to them committing the offence
- Recommendations relating to courses of training or treatment which might assist the rehabilitation of the offender
- An assessment of the risk of further offending
- A recommendation as to the appropriate penalty, including proposed terms and conditions for the offender's supervision, training and treatment within the community whether immediately or upon release from prison
A number of programmes designed to assist offenders are also available.  For example, Straight Thinking is a programme aimed at promoting life skills needed to avoid further offending and STOP is a programme designed to address the causes of violence. Probation officers may mention these in a pre-sentence report and recommend that the offender attend one of these courses to address their offending behaviour.
Judges may also ask for psychiatric and psychological reports, which are commonly obtained for offenders who have mental health and/or drug or alcohol addiction problems.
For much of our history, victims did not have specific rights at sentencing and there was no formal mechanism for them to express their feelings to the Court prior to sentencing. The Victims Rights Act 2002 addressed these issues and created the right to provide a victim impact statement.  It is not compulsory but gives the victim an opportunity to tell the Court how the offending has impacted them. This statement details any physical injuries, property loss and other effects (particularly psychological impacts), suffered by the victim. The statement is either read by the judge before the sentencing, or, with leave of the judge, may be read in open court by the victim and in the presence of the offender before sentence is imposed. Certain victims, such as victims of serious assaults or sexual crimes, are entitled to read their statements as a right (unless the judge considers it inappropriate to do so). 
Victims support volunteers are also available at courthouses to help victims understand and deal with the court process. Victims must be treated with courtesy and compassion, they are entitled to information concerning the court process and also have specific protections for their privacy.
The facts of the case have a major bearing on the sentence imposed. Where an offender pleads not guilty and the case is the subject of a defended hearing, the judge who presided at the trial will impose a sentence based on the evidence that is heard at trial.
Where an offender pleads guilty, the prosecution will provide a summary of facts for sentencing. if the defence disagrees with this summary, the judge can hold a disputed facts hearing to resolve the issue . The judge will then hear evidence about the offending and will make factual findings in the same way as if a full trial had occurred.
Offenders are sentenced in open court. Members of the public and media representatives may attend. Before the hearing, the judge will read any reports prepared for sentencing purposes including written submissions filed by lawyers representing the Crown (the prosecution) and the offender.
In addition, the lawyers may also make oral submissions at the hearing. This provides an opportunity for the lawyers to emphasise points of particular importance to their respective cases. Counsel appearing for the Crown may draw attention to particular facts of the case, aggravating features (that the offender was in a position of trust in relation to the victim, that the victim was particularly vulnerable etc), whether the offence is prevalent either nationally or locally, and what form of sentence and sentencing range is considered appropriate in all the circumstances of the case.
Counsel appearing for the offender may emphasise mitigating features (the youth of the offender, extenuating circumstances which existed at the time of the offence etc) and also endeavour to persuade the judge as to the form of penalty and, where appropriate, its length. Either lawyer may also make submissions about other relevant issues such as whether the offender should be allowed to apply for home detention.
Once the oral submissions are completed, the judge will hand down the sentence. The judge will orally explain the reasons for the sentence and formally sentence the offender.
The judge’s sentencing remarks are directed at a range of different people. The offender, of course, is entitled to be told why the particular sentence is being imposed. But in addition the victim, the Crown and the public also have a legitimate interest in the sentencing outcome. The judge will often try and explain the sentence for the benefit of the public at large (if likely to be reported by the media), so that people can understand the consequences of offending. The judge will also be conscious that the sentence may be considered for an appeal; in which case the sentencing decision will be scrutinised by another court to ensure that the sentence was reached correctly.
A major consideration in arriving at a particular sentence is the need for consistency. Although the circumstances of different cases and different offenders are never the same, it is nonetheless a requirement of sentencing that the sentences imposed by different judges are generally consistent. Because different cases are never identical, individual sentences are required to fall within what is often termed the "acceptable range" of sentences for that offence. There is, therefore, scope for the judge to take account of factors personal to the offender, provided that the sentence remains within the permitted range.
While the Court of Appeal does not sentence defendants, it has a role in correcting sentences which it considers to be wrong and giving sentencing guideline judgments.
The Court of Appeal may correct sentences if, for example, it considers the sentence is outside the available range for the particular offence, or is otherwise wrong (for instance that a principle in the Sentencing Act has not been applied or a relevant fact has been ignored).
The Court of Appeal is best placed to give sentencing guideline judgments because the Court of Appeal judges review different decisions from all over the country.
A guideline judgment typically contains a review of the sentences imposed for a particular offence in past cases. The court draws on the past cases to establish a sentencing range, to try and increase consistency in future sentences for the same offence. The guideline judgment may also identify and assess common features of the offence, to guide judges as to where individual cases fall within the available range.
From time to time, particularly where the maximum penalty for an offence has been increased by Parliament or where an offence has become more common, the Court may reconsider and issue a new guideline judgment to alter the sentencing range for an offence.
There are some offences for which the Court of Appeal has considered it inappropriate to prescribe a sentencing range. One example of this is manslaughter - the maximum penalty for manslaughter is life imprisonment. The worst cases of manslaughter are near to murder and can attract very severe sentences of imprisonment. But a conviction for manslaughter may also result where someone causes the death of another person by accident, without intending any harm, meaning that sentence of imprisonment may be inappropriate. Given the wide range of circumstances that can all fall within “manslaughter”, it is not possible to provide a single guideline that addresses all cases. In sentencing for manslaughter Judges take guidance instead from earlier cases involving manslaughter of a generally similar kind.
How sentencing works: view a Law Society video explaining the sentencing process and how judges are required to approach sentencing
New Zealand Law Society criminal law committee convenor Steve Bonnar QC outlines sentencing considerations and how judges are required to approach sentencing:
 and Sentencing Act 2002
 , the Hon JJ Spigelman, Address to the National Conference of District and County Court Judges, Sydney, 24 June 1999