Subtitles are texts representing the contents of the audio in a film, television show, opera or other audiovisual media. Subtitles might provide a transcription or translation of spoken dialogue. Although naming conventions can vary, captions are subtitles that include written descriptions of other elements of the audio, like music or sound effects. Captions are thus especially helpful to deaf or hard-of-hearing people. Subtitles may also add information that is not present in the audio. Localizing subtitles provide cultural context to viewers. For example, a subtitle could be used to explain to an audience unfamiliar with sake that it is a type of Japanese wine. Lastly, subtitles are sometimes used for humor, as in Annie Hall, where subtitles show the characters' inner thoughts, which contradict what they were saying in the audio.

Creating, delivering, and displaying subtitles is a complicated and multi-step endeavor. First, the text of the subtitles needs to be written. When there is plenty of time to prepare, this process can be done by hand. However, for media produced in real-time, like live television, it may be done by stenographers or using automated speech recognition. Subtitles written by fans, rather than more official sources, are referred to as fansubs. Regardless of who does the writing, they must include information on when each line of text should be displayed.

Second, subtitles need to be distributed to the audience. Open subtitles are added directly to recorded video frames and thus cannot be removed once added. On the other hand, closed subtitles are stored separately, allowing subtitles in different languages to be used without changing the video itself. In either case, a wide variety of technical approaches and formats are used to encode the subtitles.

Third, subtitles need to be displayed to the audience. Open subtitles are always shown whenever the video is played because they are part of it. However, displaying closed subtitles is optional since they are overlaid onto the video by whatever is playing it. For example, media player software might be used to combine closed subtitles with the video itself. In some theaters or venues, a dedicated screen or screens are used to display subtitles. If that dedicated screen is above rather than below the main display area, the subtitles are called surtitles.

Sometimes, mainly at film festivals, subtitles may be shown on a separate display below the screen, thus saving the filmmaker from creating a subtitled copy for just one showing.

Professional subtitlers usually work with specialized computer software and hardware where the video is stored digitally, making each frame instantly accessible. Besides creating the subtitles, the subtitler usually tells the computer software the timing and duration of each subtitle. These markers are usually based on timecode if it is a work for electronic media (e.g., TV, video, DVD) or on film length (measured in feet and frames). For cinema exhibition, this task is undertaken by a specialist or team of specialists.

The finished subtitle file is used to add the subtitles to the picture, either:

Subtitles can also be created by individuals using freely available subtitle-creation software such as Subtitle Workshop, MovieCaptioner, and Subtitle Composer, and then hardcode them onto a video file with software such as VirtualDub in combination with VSFilter (which could also be used to show subtitles as softsubs in many software video players).