Yesterday, after writing about half whole-wheat pretzel rolls, a coworker called me with the question: "What's vital wheat gluten?"
I thought I'd blogged about it before, but it turns out, I've just mentioned it a lot.
According to Bob's Red Mill , which sells the stuff, it's "the natural protein found in wheat. It contains 75 percent protein. A small amount added to yeast bread recipes improves the texture and elasticity of the dough. This is often used by commercial bakeries to produce light textured breads, and can easily put the home bread baker on a par with the professionals."
It looks like flour, but isn't. It helps doughs, especially doughs containing whole-wheat flour, rise better. I find that when I use it, the texture in my whole-wheat baked goods is much smoother and more like an all-white flour product. It helps my baked good rise beautifully.
I also substitute some vital wheat gluten in with white flour when making a recipe that calls for bread flour. (A quick Google search also reveals you can use it to make seitan , but I've never done so.)
I tend to use a tablespoon for two or three cups of whole-wheat flour (although a review of recipes I've posted on this blog, the amount I use tends to vary wildly). I find I sometimes need to add more water when using it, or I try to use a tablespoon less of flour if adding a tablespoon of vital wheat gluten.
I buy mine at Beachy's Bulk Foods in Arthur. 
Along with Bob's Red Mill, it looks like Hodgson Mill , King Arthur Flour  and Arrowhead Mill s all sell vital wheat gluten. I'd be willing to bet you can find it at grocery stores with well-stocked baking sections, or in local health-food stores.
Here are my previous blog posts that that call for vital wheat gluten: