Sámi reindeer husbandry in Norway is divided into 89 districts. A district is an administrative unit which includes a specific geographical area and whose main task is to organize reindeer husbandry within the district. The districts where established in 1978 and from the beginning, the districts were established so that liability for wrongful conduct could be placed on the reindeer owners collectively within a naturally defined reindeer grazing area. A district is not a legal entity which can borrow money or issue a contract, but a district can represent individual reindeer herders in any disputes.

The New Norwegian reindeer husbandry act from 2007 has retained the system of districts but has incorporated some parts of the traditional siida system and places the Siida and the Siida unit (Siida oassi) at the centre. In the Act, the Siida is understood as one or several groups of reindeer owners within a district engaged to carry out the practical work with reindeer in a given area. The work within a Siida can be seasonally orientated, like a summer or winter Siida or be a year round Siida. In the Act, the Siida unit is understood as a family which, or an individual who, represents a unit within the district and are/is engaged in reindeer herding in a Siida with leadership of an individual, a married couple or a couple living together. The system of Siida units, or operational units (driftsenhet) as they were named until 2007, was introduced by a desire to monitor the industry and to keep control of reindeer numbers. Sámi who do not belong to a Siida unit fall outside the legal bounds now established for reindeer husbandry in Norway.

In order to lead a Siida unit, a person is required to have reindeer husbandry as his or hers main profession. The leader of a Siida unit determines who may own reindeer in the unit and how many reindeer can be owned within the unit. Members of one unit may not have reindeer in other units. Only a minor whose parents do not live together can have reindeer in his own earmark in the units in which the mother and father belong to. In Norway, as of 2006/2007, there are a total of 556 Siida units which have a member total of 2 936 people. Of these, 403 Siida units and 2 200 persons are in Finnmark, making it the most numerically significant region for reindeer husbandry in Norway.

The Siida unit leaders in a district can, if they agree, decide to establish a new Siida unit within the district. But this decision must take into account that the new Siida unit will not threaten the district's ability to conduct an ecological, economic and culturally sustainable reindeer husbandry. The area board (Områdesstyret) takes the final decision on the establishment of a Siida unit. The average age of a Siida unit leader in Norway is 45.