In which date was cannabis legalized in the Netherlands? I mean the introduction of coffee shops
Contrary to popular myth, cannabis is not legal in the Netherlands. But the current de facto liberal policy dates to 1976.
In 1976 the Netherlands adopted a formal written policy of non-enforcement for violations involving possession or sale of up to 30 grams of cannabis.  (emphasis mine)
That study I cited is worth perusing if you're interested in the subject.