Blissymbols was developed after the Second World War by Charles Bliss, to facilitate communication between speakers of different languages. It has also been used to help people with severe speech impediments to communicate without the need to speak, although Bliss did not approve of this usage. It is used in particular by people who struggle both to speak and to read or spell. The system consists of 4,000 symbols representing various abstract and concrete concepts. The symbols are not related in any way to the pronunciation of a word, so can be used in conjunction with any spoken language.

The symbols are derived from standard geometric shapes and are either pictographs, such as a jagged line to represent the concept electricity, or ideographs, such as a triangle to represent the concept creation.

Symbols can be combined to represent additional concepts, for example, the symbols for house and money can be combined to represent bank. In these cases, there is a correct, standardized order in which to write the combinations of symbols.

Symbols can also be superimposed on top of one another, for example, the symbol for mouth can be superimposed onto nose to represent taste. Some symbols have an arbitrary shape, such as the articles a/an and this.

The meaning of a symbol is determined not only by its shape but by its size. For example, a full-size circle represents the concept sun, and a half-size circle represents mouth. Sometimes visually similar symbols are also semantically related, for example a full-size upside-down ‘v’ represents action, but the same symbol half the size represents activity.

The position and orientation of a symbol can also affect its meaning. A horizontal dash at the baseline represents ground, but slightly higher it represents sky. A single symbol is also used to represent both steam (pointing upwards) and rain (pointing downwards).

Punctuation marks, similar to those used in the Latin script but sometimes differing in proportion, are also used. A space half the width of a symbol is left between a word and any following punctuation mark. A space the width of a symbol is left between two words.

Blissymbols does not benefit from the use of a wide variety of fonts, as consistency is important in order for the symbols to be understood.