Fingerspelling (or dactylology) is the representation of the letters of a writing system, and sometimes numeral systems, using only the hands. These manual alphabets (also known as finger alphabets or hand alphabets) have often been used in deaf education and have subsequently been adopted as a distinct part of a number of sign languages. There are about forty manual alphabets around the world. Historically, manual alphabets have had a number of additional applications—including use as ciphers, as mnemonics and in silent religious settings.

As with other forms of manual communication, fingerspelling can be comprehended visually or tactually. The simplest visual form of fingerspelling is tracing the shape of letters in the air and the simplest tactual form is tracing them on the hand. Fingerspelling can be one-handed such as in American Sign Language, French Sign Language and Irish Sign Language, or it can be two-handed such as in British Sign Language.

Fingerspelling has been introduced into certain sign languages by educators and as such has some structural properties that are unlike the visually motivated and multi-layered signs that are typical in deaf sign languages. In many ways fingerspelling serves as a bridge between the sign language and the oral language that surrounds it.

Fingerspelling is used in different sign languages and registers for different purposes. It may be used to represent words from an oral language that have no sign equivalent or for emphasis or clarification or when teaching or learning a sign language.

In American Sign Language (ASL) more lexical items are fingerspelled in casual conversation than in formal or narrative signing. Different sign language speech communities use fingerspelling to a greater or lesser degree. At the high end of the scale fingerspelling makes up about 8.7% of casual signing in ASL and 10% of casual signing in Auslan. The proportion is higher in older signers. Across the Tasman Sea only 2.5% of the corpus of New Zealand Sign Language was found to be fingerspelling. Fingerspelling did not become a part of NZSL until the 1980s. Before that words could be spelled or initialised by tracing letters in the air. Fingerspelling does not seem to be used much in the sign languages of Eastern Europe except in schools, and Italian Sign Language is also said to use very little fingerspelling, and mainly for foreign words. Sign languages that make no use of fingerspelling at all include Kata Kolok and Ban Khor Sign Language.

The speed and clarity of fingerspelling also vary among different signing communities. In Italian Sign Language fingerspelled words are produced relatively slowly and clearly, whereas fingerspelling in standard British Sign Language (BSL) is often rapid so that the individual letters become difficult to distinguish and the word is grasped from the overall hand movement. Most of the letters of the BSL alphabet are produced with two hands but when one hand is occupied the dominant hand may fingerspell onto an imaginary subordinate hand and the word can be recognised by the movement. As with written words, the first and last letters and the length of the word are the most significant factors for recognition.

When people fluent in sign language read fingerspelling they do not usually look at the signer's hand(s) but maintain eye contact, as is normal for sign language. People who are learning fingerspelling often find it impossible to understand it using just their peripheral vision and must look straight at the hand of someone who is fingerspelling. Often they must also ask the signer to fingerspell slowly. It frequently takes years of expressive and receptive practice to become skilled with fingerspelling.

Power et al. (2020) conducted a large-scale data study into the evolution and contemporary character of 76 current and defunct manual alphabets (MAs) of sign languages, postulating the existence of eight groups: an Afghan–Jordanian Group, an Austrian-origin Group (with a Danish Subgroup), a British-origin Group, a French-origin Group, a Polish Group, a Russian Group, a Spanish Group, and a Swedish Group. Notably, several defunct versions of German, Austrian, Hungarian and Danish manual alphabets were part of the Austrian-origin group, while the current MAs of these sign languages are closely related to the French, American, International Sign and other MAs in the French-origin Group. Latvian Sign Language's MA dangled somewhere between the Polish and Russian Groups, Finnish Sign Language (which belongs to the Swedish Sign Language family) had a French-origin MA, while Indo-Pakistani Sign Language (whose lexicon and grammar have independent origins) currently used a two-handed manual alphabet of British origin.