From BlenderWiki

Basic selection

The most common way to select an element, whatever select mode you are using, is to RMB on that item, exactly as with objects in Object mode. This will replace the existing selection with the new item.

To add to the existing selection hold down ⇧ Shift while right clicking. Clicking again on a selected item will de-select it.

As in Object mode, there is a unique active element, displayed in a lighter shade (in general, the last element selected). Depending on the tools used, this element might be very important!

Note that there is no option to choose what element to select between overlapping ones (like the AltRMB click in Object mode). However, if you are in solid, shaded, or textured viewport shading mode (not bounding box or wireframe), you will have a fourth button that looks like a cube, just right to the select mode ones. When enabled, this limits your ability to select based on visible elements (as if the object was solid), and prevents you from accidentally selecting, moving, deleting or otherwise working on backside or hidden items.

Keep in mind that when you select explicitly some elements of one kind, either by this simple way, or using more advanced tools described later on, you also implicitly select the elements of other types that are involved or defined by your explicit selection, as described in the previous page.

Selecting elements in a Region

This is also more or less the same tools as for Object mode selection. But in addition to rectangular (box) and lasso selection, you have a sort of “paint” circular selection.

See the object selection page for border and lasso selection – there is nearly no difference between Object and Edit modes here.

There is just a small tricky point to take into account:

• When in Vertex select mode, no problem, vertices are punctual, so they must be inside the region to be selected.
• With Edge select mode, these tools behave somewhat differently than in Object mode: any edge that is even partly inside the region will be selected.
• For Face select mode, they behave exactly as in Object mode – only faces of which center (selection point) is inside the region will be selected.

Circular region

This selection tool is only available in Edit mode and can be activated with B, B. That is, pressing the B key twice in a row. Once in this mode the cursor changes to a dashed cross-hair with a 2D circle surrounding it. The tool will operate on whatever the current select mode is. Clicking or dragging with the LMB , when elements are inside the circle, will cause those elements to be selected.

You can enlarge or shrink the circle region using + NumPad and - NumPad, or the Wheel .

(Circle Region Select) is an example of selecting edges while in Edges select mode. As soon as an edge intersects the circle the edge becomes selected. The tool is interactive such that edges are selected while the circle region is being dragged with the LMB .

If you want to de-select elements either hold MMB or AltLMB and begin clicking or dragging again.

For Faces select mode, the circle must intersect the face indicators usually represented by small pixel squares; one at the center of each face.

As usual, to exit from this tool click RMB , or hit the Esc key.