Usually owned by the local council (State) and rented at a nominal rent (way below market value). Originally intended so working folk had enough land to grow food for their families.
... Finally, a bit of allotment trivia. Einstein used to have an allotment/tuin when he was living in the Netherlands, and he got a letter from the Allotment society asking him to either tidy his tuin, or to vacate the plot. ...