The Canadian Wheat Board is the world's largest single seller of wheat and barley, accounting for 20% of the global market.
It was formed in response to the tremendous poverty of Western Canadian farmers during the Great Depression. Individual (small) farmers were powerless, and had to take whatever they could get for their crops. By having one entity, the CWB, sell the crops of thousands of farmers, they could obtain much better prices for their wheat and barley.
Membership is mandatory in three provinces and part of a fourth. This gives the CWB the clout it needs in global grain markets.
At least one farmer would like the Canadian Wheat Board to leave him alone. Hearing the reasons why is interesting, and of special value to economics undergraduates learning about perfect competition and monopoly.