Buttons are objects in the Mario & Luigi series. When struck, usually a event occurs in the area. Although their exact functions vary throughout the series, the gimmick follows. Besides this, buttons display other uses.
Buttons are first shown in Mario & Luigi: Superstar Saga, through locations in the Beanbean Kingdom. They function like switches with many purposes, each one revealed when the button's hit. This usually result in opening gates, doors, or other barriers, though occasionally nearby elements in the environment are affected, such as having a barrel appear.
Buttons return in Mario & Luigi: Partners in Time, functioning in the same manner. They can now be struck and activated with anybody's hammer, and are usually meant to help the player progress when hit
In Mario & Luigi: Bowser's Inside Story, buttons know as Nubbins appear throughout Bowser's body, and function in the same way as regular buttons, typically triggering some sort of event or unlocking a nearby area.
Buttons appear throughout the newer series as well with the same purposes.