单元音是指发音时舌位、唇形保持不变的单个元音，又称纯元音，属于语言文字学科范畴。英语中共有12个单元音，根据发音时舌面最高点位置分为前元音、中元音和后元音三类，其中前元音包括/iː/、/ɪ/、/e/、/æ/，中元音包括/ə/、/ɜː/、/ʌ/，后元音包括/ɑː/、/ɔː/、/ɒ/、/uː/、/ʊ/，按发音时长可分为5个长元音和7个短元音。发音特征涉及舌尖位置、口型开合及唇形圆展，例如前元音/iː/发音时舌尖抵下齿，舌前部抬起呈微笑状；后元音/ɑː/需舌身后缩，口型自然张大。

单元音发音时可按舌面隆起的位置分为前元音，后元音和中元音三类。发前元音时舌的最高点在口腔的前部；发后元音时，舌的最高点在口腔的后部；发中元音时舌的最高点在口腔的中部。

以英语元音为例

前元音: [i:] [ i] [ e ] [æ]

中元音: [ʌ][ə:][ə]

后元音: [ɔ] [ɔ:] [u:] [u] [a:]

[i:] sea, he, see, piece, ceiling, street, beef, these, week, meat, agree

[ɪ]sit, build, miss, myth, palace, between, if, give, busy, gym

[e] bed, desk, head, anything, many, again, special, heavy, weather, whether, friendly

[æ] bad, land, bank, stamp, pal, Canada, taxi

[a:] car, fast, class, plant, calm, aunt

[ ɔ] hot, want, wallet, wash, what

[ ɔ:] door, more, sport, ball, warm, author, court, bought, caught

[u:] who, blue, soup,

[u] look, put, woman, could，good

[ʌ] cup, come, blood, rough

[ə:] girl, work, serve, nurse

[ə ] cadre, ago, forget, polite, dollar, doctor, famous, Saturday

汉语普通话

拼音：a o e i u ü er

这几个元音音位还有各自的音位变体

e[ɤ] 在i和ü后的实际发音为[ê]

i 在声母jqx后的实际发音为[ɩ]，而在声母zh ch sh r后的实际发音又为[ɿ]

关于韵母er，虽然由两个字母组合而成，但却是卷舌的单元音[ə˞]（舌位没有变化）

[i:] sea, he, see, piece, ceiling, street, beef, these, week, meat, agree

[ɪ]sit, build, miss, myth, palace, between, if, give, busy, gym

[e] bed, desk, head, anything, many, again, special, heavy, weather, whether, friendly

[æ] bad, land, bank, stamp, pal, Canada, taxi

[a:] car, fast, class, plant, calm, aunt

[ɔ] hot, want, wallet, wash, what

[3:] skirt，bink，girl,person,purple,learn

[u:] good, who, blue, soup,

[u] look, put, women, could

[ʌ] cup, come, blood, rough，up

[ə:] girl, work, serve, nurse

[ə] cadre, ago, forget, polite, dollar, doctor, famous, Saturday