Speech balloons (also speech bubbles, dialogue balloons or word balloons) are a graphic convention used most commonly in comic books, comics and cartoons to allow words (and much less often, pictures) to be understood as representing the speech or thoughts of a given character in the comic. There is often a formal distinction between the balloon that indicates thoughts and the one that indicates words spoken aloud: the balloon that conveys thoughts is often referred to as a thought bubble.
One of the earliest antecedents to the modern speech bubble were the "speech scrolls", wispy lines that connected first person speech to the mouths of the speakers in Mesoamerican art between 600 and 900 AD.
In Western graphic art, labels that reveal what a pictured figure is saying have appeared since at least the 13th century. These were in common European use by the early 16th century. Word balloons (also known as "banderoles") began appearing in 18th-century printed broadsides, and political cartoons from the American Revolution (including some published by Benjamin Franklin) often used them. They later fell out of fashion, but by 1904 had regained their popularity, although they were still considered novel enough to require explanation. With the development of the comics industry in the 20th century, the appearance of speech balloons has become increasingly standardized, though the formal conventions that have evolved in different cultures (USA as opposed to Japan, for example), can be quite distinct.
Richard F. Outcault's Yellow Kid is generally credited as the first American comic strip character. His words initially appeared on his yellow shirt, but word balloons very much like those in use today were added almost immediately, as early as 1896. By the start of the 20th century, word balloons were ubiquitous, and since that time only a very few comic strips and comic books have relied on captions, notably Hal Foster's Prince Valiant and the early Tarzan comic strip. For many years, word balloons were less common in Europe than in the USA, or were used together with captions. (One example is the Dutch cartoonist Marten Toonder's comics about Tom Puss and Oliver B. Bumble, where the literary captions are printed out below the strip and almost take up as much space as the drawings, so that the strip fills twice the space of most newspaper strips. A similar example from the UK is Rupert Bear.)