Speech balloons (also speech bubbles, dialogue balloons, or word balloons) are a graphic convention used in comic books, strips, 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 bubble that conveys subjective thoughts is often referred to as a thought balloon.

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 Late Classic era (600-900 CE) Mayan art.•

In Western graphic art, labels that reveal what a pictured figure is speaking have appeared since at least the 13th century. More recognizably modern "speech balloons" begin appearing in 17th century printed broadsides. 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.

The Yellow Kid is generally credited as the first true 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 the use of word balloons was 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 England is Rupert the Bear.

Some characters and strips use highly unconventional methods of communication. Perhaps the most notable is the Yellow Kid, an early American comic strip. His (but not the other characters') words would appear on his large, smock-like shirt.

Also noteworthy are the many variations on the form created by Dave Sim for his comic Cerebus the Aardvark. Depending on the shape, size, and position of the bubble, as well as the texture and shape of the letters within it, Sim could convey large amounts of information about the speaker. This included separate bubbles for different states of mind (drunkenness, etc), for echoes, and a special class of bubbles for one single floating apparition.

An early pioneer in experimenting with many different types of speech balloons and lettering for different types of speech was Walt Kelly, in his Pogo strip.

In the famous French comic series Asterix, Goscinny and Uderzo use bubbles without tails to indicate a distant or unseen speaker. They also have had fun experimenting with many different types of lettering to suit characters with distinct nationalities, thus meaning they speak a different language that Asterix may not understand, but the readers can. So Goths spoke in a "black letter" font, Greek had a more angular font than normal, Norse used "Nørdic åccents", Egyptian was in faux hieroglyphics etc. Another original experiment with speech bubbles was exclusive to one album, Asterix and the Roman Agent. The agent in question was a vile manipulator who could create dissention amongst any group of people with a single innocent-sounding comment. His victims start quarreling and ultimately fighting each other while speaking in green-colored speech bubbles, which symbolize darnel.

Font variation is a common tactic in comics. The Sandman series, written by Neil Gaiman, features many characters whose speech bubbles are written with a font that is exclusive to them. Some examples: the main character, the gloomy Dream speaks in wavy-edged bubbles, completely black, with similarly wavy white lettering. His sister, the scatterbrained and whimsical Delirium speaks in bubbles in a many-colored explosive background with uneven lettering, and the irreverent raven Matthew speaks in a shaky angular kind of bubble with scratchy lettering. Other characters, such as John Dee, have special shapes of bubbles for their own.

In MAD Magazine, in the recurring "Monroe" comic strip, certain words are written larger or in unusual fonts for emphasis.

In manga, there is a tendency to include the speech necessary for the storyline in balloons, while small scribbles outside the balloons add side comments, often used for irony or to show that they're said in a much smaller voice. Satsuki Yotsuba in the manga series Negima is notable because she speaks almost entirely in side scribble.

In the silent film Life of a Tennis Ball (film), the director used "subtle subtitles" to convey dialogue much in the same way as speech balloons in comics. Lines of dialogue were positioned in frame according to the source of the line, and also so that the lines may be read left to right, top to bottom. Some lines faded, rather than cut away, to emphasize emotions.