This list contains acronyms, initialisms, and pseudo-blends  that begin with the letter Y.

For the purposes of this list:

• acronym = an abbreviation pronounced as if it were a word, e.g., SARS = severe acute respiratory syndrome, pronounced to rhyme with cars
• initialism = an abbreviation pronounced wholly or partly using the names of its constituent letters, e.g., CD = compact disc, pronounced cee dee
• pseudo-blend = an abbreviation whose extra or omitted letters mean that it cannot stand as a true acronym, initialism, or portmanteau (a word formed by combining two or more words).

(a) = acronym, e.g.: SARS – (a) severe acute respiratory syndrome

(i) = initialism, e.g.: CD – (i) compact disc

(p) = pseudo-blend, e.g.: UNIFEM – (p) United Nations Development Fund for Women

(s) = symbol (none of the above, representing and pronounced as something else; for example: MHz – megahertz)

Some terms are spoken as either acronym or initialism, e.g., VoIP, pronounced both as voyp and V-O-I-P.

(Main list of acronyms)

• y – (s) Yocto-
• Y – (s) Yotta – Yttrium

• Y2K – (i) Year Two Thousand

• yA – (s) Yoctoampere
• Ya – (s) Yottayear
• YA
  • (s) Yottaampere
  • (i) Young Adult
• YAC – (a/i) Youth-Adult Committee
• YAFLA – (a) Yet Another Five Letter Abbreviation
• YAP – (a) Young Aspiring Professional
• YaBPr – (a) Yet another Brother Pat rant
• YABSLAG – (a) Yet another boy singing like a girl

• Yb – (s) Ytterbium
• YB – (i) Youcef Benzouada (Southern Algerian name)

• yC – (s) Yoctocoulomb
• YC – (s) Yottacoulomb

• YD – (s) People's Democratic Republic of Yemen (ISO 3166 digram, obsolete 1990)
• YDS – (i) Yosemite Decimal System (climbing)

• YE – (s) Yemen (ISO 3166 digram)
• YEM – (s) Yemen (ISO 3166 trigram) – Manitowaning/Manitoulin East Municipal Airport IATA airport code
• YER – (s) Yemeni rial (ISO 4217 currency code)

• yF – (s) Yoctofarad
• YF – (s) Yottafarad

• yg – (s) Yoctogram
• Yg – (s) Yottagram
• YGM – You've got mail
• Ygo – (i) Yu-Gi-Oh!
• YGCO – (i) Yamaneko Group of Comet Observers

• yH – (s) Yoctohenry
• YH – (s) Yottahenry
• YHS – Ya Hoor sur!
• YHBT – (i) You Have Been Trolled
• YHIH1 – (a) You Heard It Here First (lowercase: yhih1, pronounced yi-hi)
• YHII – You Have It Inside

• yi – (s) Yiddish language (ISO 639-1 code)
• Yi – (s) Yobi
• YI – (s) Serbia and Montenegro (deprecated FIPS 10-4 country code, now RB (Serbia) and MJ (Montenegro))
• yid – (s) Yiddish language (ISO 639-2 code)
• YIH – (a) Yiff In Hell
• YILP – (a) Youth Integration Livelihood Improvement Project
• Yippie – (p) Youth International Party + suffix

• yJ – (s) Yoctojoule
• YJ – (s) Yottajoule

• yK – (s) Yoctokelvin
• YK – (s) Yottakelvin
• YKYFCW – You know you're from Christchurch when (post-earthquake joke)

• yL – (s) Yoctolitre
• YL – (s) Yottalitre

• ym – (s) Yoctometre
• Ym – (s) Yottametre
• YM – (s) Yemen (FIPS 10-4 country code) – (i) Your Magazine (originally Young Miss, later Young & Modern)
• YMCA – (i) Young Men's Christian Association
• YMD – (s) People's Democratic Republic of Yemen (ISO 3166 trigram, obsolete 1990)
• YMMD – (i) You Make My Day
• YMMV – (i) Your Mileage May Vary (adapted from the EPA's automobile mileage estimates, where it is used to convey the original meaning, "results may vary"); but (now) when used as an idiom, it -- (either the acronym "YMMV" or the 4 words) -- can instead mean (this e.g. comes from wikt:your mileage may vary#Phrase:) "this is just my opinion, your opinion may be different".

• yN – (s) Yoctonewton
• YN – (s) Yottanewton
• YNWA – reference to Liverpool F.C.'s sports anthem, the 1945 show tune You'll Never Walk Alone

• yo – (s) Yoruba language (ISO 639-1 code)
• YO – (s) former Yugoslavia (NATO country code, obsolete 1993)
• YOLO – (a) You Only Live Once
• yor – (s) Yoruba language (ISO 639-2 code)

• YPA – (i) Yards per Pass Attempt (football statistic)
• YPG – (i) Yekîneyên Parastina Gel (Kurdish, "People's Protection Units" or "People's Defense Units")
• YPIO – (a) Your Problem Is Obvious
• YPO – (a) Young Presidents' Organization

• YRR – (i) "Young, Restless, and Reformed", an alternative name for the New Calvinist movement

• ys – (s) Yoctosecond
• yS – (s) Yoctosiemens
• Ys – (s) Yottasecond
• YS – (s) Yottasiemens
• YSA
  • (i) Young Single Adult, a designation used by the LDS Church for single adults under 30
  • Young Socialist Alliance
  • Youth Service America

• yT – (s) Yoctotesla
• YT
  • (s) Mayotte (ISO 3166 digram)
  • Yottatesla
  • Yukon Territory (postal symbol)
• YTD – (i) Year-To-Date
• YTM – (i) Yield to Maturity
• YTS – (i) Youth Training Scheme
• YTT – Yoshi Topsy-Turvy
• YT – YouTube

• YU
  • (i) York University
  • (s) former Yugoslavia (ISO 3166 digram, obsolete 2003)
• YUG – (s) former Yugoslavia (ISO 3166 trigram, obsolete 2003)
• Yuppie – (p) Young Urban Professional + suffix

• yV – (s) Yoctovolt
• YV – (s) Yottavolt

• yW – (s) Yoctowatt
• YW – (s) Yottawatt
• YWCA – (i) Young Women's Christian Association
• YWMV – (i) Your Wallet May Vary (to convey "our budgets are different as far as what is affordable / justifiable")

• YYH
  • (i) YuYu Hakusho
  • (s) Taloyoak Airport, IATA airport code
• YYK – (i) Yeah you know