Constructed scripts and traditional "natural" writing systems
All scripts, including traditional scripts ranging from Chinese to Arabic script, are human creations. However, scripts usually evolve out of other scripts rather than being designed by an individual. In most cases, alphabets are adopted, i.e. a language is written in another language's script at first, and gradually develops peculiarities specific to its new environment over the centuries. Construction of a script presupposes that the author is aware of at least one writing system already. Otherwise, the invention would not just comprise a script, but the concept of writing itself. Therefore, a constructed script is always informed by at least one older writing system, making it difficult in some cases to decide whether a new script is simply an adoption or a new creation. In the rare cases where a script evolved not out of a previous script, but out of proto-writing, the process was nevertheless a gradual evolution of a system of symbols, not a creation by design.
Overview of constructed writing systems
For previously unwritten languages
Some, like the Korean Hangul, Cherokee, N'Ko, Fraser, Tangut and Pollard scripts, were invented to allow certain spokennatural languages that did not have adequate writing systems to be written. Armenian, Georgian, and Glagolitic may fit in this category, though their origin is not known.
The best-known constructed scripts dedicated to fictional languages are J. R. R. Tolkien's elaborate Tengwar and Cirth, but many others exist, such as the Klingon script from Star Trek, Aurebesh from Star Wars, D'ni from the Myst series of video games, and the Orokin language from the video gameWarframe.
For technical purposes
Several writing systems have been devised for technical purposes by specialists in various fields. One of the most prominent of these is the InternationalPhonetic Alphabet, used by linguists to describe the sounds of human language in exhaustive detail. While based on the Latin alphabet, IPA also contains invented letters, Greek letters, and numerous diacritics. The Shavian alphabet has been designed to have an easier writing system for English.
Some neographies have been encoded in Unicode, in particular the Shavian alphabet and the Deseret alphabet. A proposal for Klingon pIqaD was turned down because most users of the Klingon language wrote it using the Latin alphabet, but both Tengwar and Cirth were under consideration in 2010. An unofficial project exists to coordinate the encoding of many constructed scripts in specific places in the Unicode Private Use Areas, known as the ConScript Unicode Registry.