Button group
Wrap a series of buttons with .btn in .btn-group
Button toolbar
Combine sets of button groups into button toolbars for more complex components
Button Sizing
Instead of applying button sizing classes to every button in a group, just add .btn-group-* to each .btn-group, including each one when nesting multiple groups.
Button Nesting
Place a .btn-group within another .btn-group when you want dropdown menus mixed with a series of buttons.