Bridge Tool

The Bridge Tool is used to generate quads that bridge between two selected edge-loops.

Operation

Preselect two sets of connected boundary edges or two sets of faces. The two sets must have the same number of vertices. Boundary edges must all have exactly one connected face. Multiple faces may be included in a face set as long as the total number of vertices for each set is the same.
Activate the Bridge Tool.
Key-in the number of bridge divisions in the measurements box OR use the up / down arrow keys to change the number of divisions.
Use the right / left arrow keys to control the twist of the bridge mesh.

Modifiers

ALT = Cycle through the interpolation modes. Use LINEAR mode for a straight bridge mesh and one of the CUBIC modes to create a curving bridge mesh.
SHIFT = Hold shift while pressing the up / down arrows to adjust the smoothness factor for cubic interpolation modes.

Example 1 - Preselect Faces

In this example, two faces are preselected prior to activating the Bridge Tool. Each face has the same number of vertices (4).

Once, the tools is activated, the bridge mesh is instantly created but you can still edit it while the tool is active. Below, the mesh has been generated using LINEAR mode and 7 divisions.

Press ALT to switch to CUBIC interpolation. This mode considers only the initial normal direction of the selected loops when generating the mesh.

Press ALT again to switch to CUBIC SURFACE interpolation. This mode takes into account the orientation of the selected loop's adjacent edges and faces when generating the bridge and tries to blend the surface smoothly.

Next, the left arrow key is pressed to create a twist and the number of divisions is increased to 16 using the up arrow key. The smoothness factor is also lowered to 0.3 by holding SHIFT and pressing the down arrow key.