Two basic options, along with two more specific variations.

Single button group

Wrap a series of buttons with .btn in .btn-group.

Multiple button groups

Combine sets of <div class="btn-group"> into a <div class="btn-toolbar"> for more complex components.

Vertical button groups

Make a set of buttons appear vertically stacked rather than horizontally.

Checkbox and radio flavors

Button groups can also function as radios, where only one button may be active, or checkboxes, where any number of buttons may be active. View the Javascript docs for that.

Dropdowns in button groups

Heads up! Buttons with dropdowns must be individually wrapped in their own .btn-group within a .btn-toolbar for proper rendering.

Use any button to trigger a dropdown menu by placing it within a .btn-group and providing the proper menu markup.

Works with all button sizes

Button dropdowns work at any size: .btn-large, .btn-small, or .btn-mini.

Requires javascript

Button dropdowns require the Bootstrap dropdown plugin to function.

In some cases—like mobile—dropdown menus will extend outside the viewport. You need to resolve the alignment manually or with custom javascript.

Split button dropdowns

Building on the button group styles and markup, we can easily create a split button. Split buttons feature a standard action on the left and a dropdown toggle on the right with contextual links.

Sizes

Utilize the extra button classes .btn-mini, .btn-small, or .btn-large for sizing.

Dropup menus

Dropdown menus can also be toggled from the bottom up by adding a single class to the immediate parent of .dropdown-menu. It will flip the direction of the .caret and reposition the menu itself to move from the bottom up instead of top down.