I will be visiting Norway during August and September. My question is: Is wild camping allowed in Norway? What are the rules, besides the obvious "take your litter with you when you leave"? Can I camp on pre-owned land?
Norway has a very extensive right-to-roam called allemannsrett. From the website of the Norwegian Environment Agency:
In open country in the lowlands, you can pitch a tent and camp overnight for up to 48 hours in one location without prior permission from the landowner. In the mountains, and in remote, sparsely populated areas, you may camp for longer than 48 hours.
So you are allowed to camp, even on private land. It goes into some more details on where you are allowed to set up camp:
Unless local bylaws provide otherwise, you must never pitch your tent within 150 metres (500 feet) of an inhabited house or cabin. Always take care not to damage young trees. Remember, you must not camp on fenced land without the landowner’s permission.
Those are the basic rules, but there is more specific advice on the website to things such as building a bonfire (not in or near woodland) and also on other rights the right-to-roam gives you, such as picking berries and mushroom.
You can camp on "out-land", which is anything not maintained/cultivated like lawns, fields, etc. I don't think ownership is an issue (no land is not owned).
In "low-land" (<200m above sea level?) you can only camp (raise a tent) for two days in the same place, in the "high-land" (everything else) there is no limit.
Here are some more details. Tent must be at least 150m from any building. There may be additional restrictions during the reindeer hunt.
(Addition: For tidsrommet umiddelbart før og under villreinjakten kan departementet på nærmere avgrenset høgfjellsområde forby eller regulere teltslåing som kan være til ulempe for villreinjakten. approx "immediately before or during the reindeer hunt, in any designated high-mountain area, tenting may be forbidden or regulated")