The English word Alphabet is based on the first two letters of the Greek Alphabet, namely, Alpha - Beta (q.v.).
The received wisdom is that the alphabet was introduced c. 1600 B.C. Recent research traces the First Alphabet (q.v.) back to c. 2000 B.C. in Egypt. The alphabet as a One Sign-One sound system of writing is said to have its origins in pictograms (cuneiform, ideograms (hieroglyphs, acrophony) and phonograms as a subset of Writing Systems.  
The roots of Western alphabets go back much further to Sanskrit, which is also a One-Sign One sound system in that every consonant is linked initially with the vowel a and can be linked systematically with other vowel sounds. Cf. the system of Aryabhatta Numeration.
Early versions of Phoenican, Hebrew and Greek have 22 Letters, which follow a regular pattern:
Beginning   - Middle - End
A                 K           T
which reflects the basic divisions in Sanskrit of
A                 K           T       P   
In Sanskrit the letters of the alphabet are linked with the basic Elements (tattvas). In the earliest systems there are 5 gross elements (earth, air, fire, water, ether). In later systems there are:
36 Consonants
36 Elements
Early versions of Phoenican, and Hebrew focus on
3 Elements                     combined with
7 Planets 
12 Signs of the Zodiac     to produce
= 22 Letters in Alphabet (q.v.)
As a result the numbers
3 7 12  and  1 11 22 33
become important in early alphabets.

Library of Congress Scope Note:
Narrower Term:  Alphabets 
Narrower Term:  Arabic alphabet 
Narrower Term:  Brahmi alphabet 
Narrower Term:  Celtiberian alphabet 
Narrower Term:  Cuneiform writing 
Narrower Term:  Cypriote syllabary 
Narrower Term:  Cyrillic alphabet 
Narrower Term:  Devanagari alphabet 
Narrower Term:  Glagolitic alphabet 
Narrower Term:  Gurmukhi alphabet 
Narrower Term:  Inscriptions, Linear A 
Narrower Term:  Jawi alphabet 
Narrower Term:  Kharosthi alphabet 
Narrower Term:  Ol alphabet 
Narrower Term:  Pasigraphy 
Narrower Term:  Phonetic alphabet 
Narrower Term:  Runes 
Narrower Term:  Siyāqat alphabet 
Narrower Term:  Bharati alphabet 
Narrower Term:  Uighur alphabet 
Narrower Term:  Rizaleo alphabet 
Narrower Term:  Dȯrvȯlzhin alphabet 
Narrower Term:  Grantha alphabet 
Narrower Term:  Tod alphabet 
Narrower Term:  X (The letter) 

Scope Note: Search also subdivision Alphabet
 or Writing under groups of languages or under particular languages, e.g. English language--Alphabet; Slavic languages--Writing; also subdivision Languages--Alphabet  under names of regions, countries, etc.
Note: Here are entered general and comparative works dealing with the Semitic alphabet and its ancient and modern derivatives, or with similar series of characters employed to represent the sounds of a language.
Note: Works on variations in the style of writing in the past, and especially with ancient and medieval handwriting, are entered under Paleography.
Note: Works on written languages as a form of communication or discourse are entered under Written communication.
Note: Works on the process or result of recording language in the form of conventionalized visible marks or graphic signs on a surface are entered under Writing.
 Works on the writing of a particular language are entered under the name of the language with subdivisions Alphabet and Writing,
e.g. Greek language--Alphabet; Egyptian language--Writing.
Works on systems of writing used by several peoples are entered under Writing,  followed by the name of the system, e.g. Writing, Arabic.

A    L     Pha     B                      E                   T
1    16   22      
                        2nd consonant   2nd vowel       Last Letter