You might think that flour is just flour; however, not all flours are created equal. You can use almost any type of flour to make a pizza, but the type of flour you use can make a difference.
Different flours have different amounts of gluten. This is the protein in wheat that helps hold in the bubbles of gas produced by the yeast. It also allows the dough to stretch as you shape the pizza. Different flours with varying amounts of gluten will behave differently; you can see and feel the difference in the dough as you mix it.
My favorite flour to use for making pizza is a mix of half All Purpose Unbleached Flour and Bread Flour. This mix provides a good balance between the extra strength of the Bread Flour with the ease of use that comes from All Purpose Unbleached Flour.