The Estonian alphabet is based on the Latin script. The Estonian orthography is generally guided by phonemic principles, with each grapheme corresponding to one phoneme.
The official Estonian alphabet has 27 letters: A, B, D, E, F, G, H, I, J, K, L, M, N, O, P, R, S, Š, Z, Ž, T, U, V, Õ, Ä, Ö, Ü.
Due to German and Swedish influence, the Estonian alphabet has the letters Ä, Ö, and Ü (A, O, and U with an umlaut), which represent the vowel sounds [æ], [ø] and [y], respectively. Unlike the German umlauts, they are considered and alphabetized as separate letters and are part of the alphabet.
The most distinctive letter in the Estonian alphabet, however, is the Õ (O with a tilde), which was added to the alphabet in the 19th century by Otto Wilhelm Masing and stands for the vowel [ɤ].
In addition, the alphabet also differs from the Latin alphabet by the addition of the letters Š and Ž (S and Z with caron/háček), and by the position of Z in the alphabet: it has been moved from the end to between S and T (or Š and Ž).
The letters F, Š, Z, Ž are so-called “foreign letters”, and occur only in loanwords and foreign proper names. Occasionally, the alphabet is recited without them and thus has only 23 letters. Where it is impractical or impossible to type Š and Ž, they are substituted with sh and zh in some written texts, although this is considered incorrect.
Additionally, C, Q, W, X, and Y are used in writing foreign proper names. They do not occur in Estonian words and are not officially part of the alphabet.
Although the Estonian orthography is generally guided by phonemic principles, with each grapheme corresponding to one phoneme, there are some historical and morphological deviations from this: for example the initial letter ‘h’ in words, preservation of the morpheme in the declension of the word (writing b, g, d in places where p, k, t is pronounced) and in the use of ‘i’ and ‘j’.
When Estonian was first written there was no standard alphabet. People used an ad hoc spelling system based on Latin and Middle Low German. In the 17th century, Bengt Gottfried Forselius and Johann Hornung created a way of writing Estonian based on German. That was replaced by a Finnish-based orthography, known as the Newer Orthography, created by Eduard Ahrens in the second half of the 19th century. This was the basis for the current orthography.