Modeling: A Million to One - Blender Foundations: The Essential Guide to Learning Blender 2.6 - page 64

Figure 4.7 Three faces created, with two more edges below.
to select faces. At the moment, that might seem like a questionable benefit, but later on when mesh models
become increasingly complex, it often makes sense to work at this level.
Anyway, with this edge selected, use the Subdivide tool, either from the T-key tool shelf on the left or
by pressing the W key to bring up the Specials pop-up menu in the 3D view. Subdivide splits the selected
geometry into two equal parts, and in this case creates a new vertex in the middle of the edge. Switching
back to Vertex select mode, either from the 3D header button or by pressing Ctrl-Tab, shows this new
vertex.
Want to see something cool? Bring up the tool shelf with the T key if it isn't already visible. At the
bottom of the shelf, you'll notice the Tweak Panel for the last operation. In this case, that's Subdivide.