Wild camping permitted - Tenting in the open countryside
In general, there is free camping (using a tent) and then there is bivouacking (e.g. under a tarp). Bivouacking is regarded as making a shakedown and is permitted as long as this shakedown is not on someones private premises without their consent. Wild camping, on the other side, is mostly forbidden in Germany and Austria; in Switzerland the regulations vary from canton to canton. So better check locally whether or not you are allowed to put up your tent anywhere in the country.
In other countries, wild camping is permitted. Maybe, your next tour should bring you to Estonia, Latvia, Lithuania or Ireland if you prefer sleeping off camping sites. In Sweden, Norway and Finland the “Allemannsretten” (everyman's right) applies. This is the right to public access to the wilderness, meaning every outdoorer is allowed to sleep outside. But there are certain rules, of course: no open fire, do not camp within sight of houses. Saving the environment obviously is a standard rule.
Exceptions prove the rule
In some places in Germany wild camping is legal. One of them is the nature park “Pfälzer Wald”. Since 2009 wild camping is permitted in certain areas off huts and hiking trails but prior registration is mandatory.
Another place is the national park “Sächsische Schweiz” - same rules apply.
The federal states of Brandenburg, Mecklenburg-Vorpommern and Schleswig-Holstein allow wild camping only for one night as long as you do not use motorised vehicles and do not make your camp in a nature reserve.