The Scottish Gaelic alphabet contains 18 letters and is the same alphabet as used in Irish Gaelic. The two languages are closely related. In fact, Gaelic was introduced to Scotland around the 4th century AD from Ireland. The proximity of the North of Ireland to the West of Scotland means that the Northern Ulster dialect in Ireland is particulary close to the dialect spoken in Scotland's Western Isles.
While the letters are the same, what distinguishes the Scottish Alphabet from the traditional Irish Gaelic alphabet is the name that each letter is given. In Irish Gaelic, they are given the standard Latin name but in Scottish Gaelic they are given the name of a tree or plant.
In addition, in the Scottish alphabet a grave accent on the vowels à, è, ì, ò, ù indicates a longer form of the vowel. In Irish Gaelic, a síne fada (acute accent) which points the other direction á, é, í, ó, ú does a similar job. Vowels with accents are not regarded as different letters. The accents are important, however, in both languages as they change both the sound and meaning of a word.
In the past, Scottish Gaelic also used these acute accents, not to indicate a change in vowel length but in vowel quality. These have, for the most part, been abandoned in the school system through a spelling reform. However, many academics oppose these changes and the traditional spelling forms are still common in universities.
Another important difference between Irish Gaelic and Scottish Gaelic is that while Irish Gaelic used its own script for printing until recent years, Scottish Gaelic has always used the Latin letters for printing. Old manuscripts in Scottish Gaelic may show a distinctive Gaelic form of writing.
Learn more about the Irish Gaelic Alphabet and the ancient Ogham system of writing here.