Do you need a composting bin to compost?

Composting doesn't require compost bins. But bins keep compostable materials from getting too wind-blown, and too wet. Specifically, the moisture level of compostable materials needs to be on par with a wrung out sponge. Compostable materials need to be turned regularly. In fact, the more often the turning, the quicker the breakdown, the sooner the end product. It's easier to turn the layers in a bin than in a pile. And, in the case of worm composting, red wigglers prefer the confined space and the closed covers.