The Select Menu

Creating Selections

Constrain to a Square Selection

Mouse: Shift + drag with the Rectangular Marquee tool

This shortcut works only if you are starting a new selection or adding Shift to a selection you are currently creating. If a selection already exists, you add to the selection instead. (See the shortcut to "Add a Square or Circle to Active Selection.")

Constrain to a Circle Selection

Mouse: Shift + drag with the elliptical marquee tool

This shortcut works only if you are starting a new selection or adding Shift to a selection you are currently creating. If a selection already exists, you add to the selection instead. (See the shortcut, "Add a Square or Circle to Active Selection.")

Draw from the Center While Creating Selections

Mac: Option + drag

Win: Alt + drag

Normally, when creating a selection, the selection anchors itself from wherever you click, creating the selection outward from that position in a diagonal direction. With this shortcut, wherever you click becomes the center of the selection as you create it. Also, remember that this shortcut works only if you are starting a new selection or when you add the modifier key after you have started the selection. If a selection already exists, you subtract from the selection instead.

Constrain and Draw from the Center While Creating Selections

Mac: Option + Shift + drag

Win: Alt + Shift + drag

Normally, when creating a selection, the selection anchors itself from wherever you click, creating the selection outward from that position in a diagonal direction. With this shortcut, wherever you click becomes the center of the selection as you create it. Also, remember that this shortcut works only if you are starting a new selection or when you add the modifier keys to a selection you have started. If a selection already exists, you are left with the intersection of the selections instead.

Constrain a Selection as You Move It

Mouse: Shift + drag

Make sure the cursor is within the selection area and that you press the mouse button down before you hold down the Shift key. If you hold down the Shift key first, you will add to the selection when you start dragging. If the cursor is outside the selected area, you will start a new selection instead of moving the existing one.

Reposition a Selection as You Create It

Both: Spacebar

This is one of my favorite shortcuts. Sometimes you are trying to select a specific shape in an image and halfway through dragging out the selection, you realize you didn't start in the right position. Rather than starting over, just hold down the Spacebar. This allows you to drag the marquee to a different position. When you are ready to continue with the selection, just let go of the Spacebar. Remember to keep the mouse button down until you are finished making the selection.