structural:reformatting, information:filtering
Segmental phonology

The Spanish phonemic inventory consists of five vowel phonemes (/a/, /e/, /i/, /o/, /u/) and 17 to 19 consonant phonemes (the exact number depending on the dialect). The main allophonic variation among vowels is the reduction of the high vowels /i/ and /u/ to glides— and respectively—when unstressed and adjacent to another vowel. Some instances of the mid vowels /e/ and /o/, determined lexically, alternate with the diphthongs /je/ and /we/ respectively when stressed, in a process that is better described as morphophonemic rather than phonological, as it is not predictable from phonology alone.

The Spanish consonant system is characterized by (1) three nasal phonemes, and one or two (depending on the dialect) lateral phoneme(s), which in syllable-final position lose their contrast and are subject to assimilation to a following consonant; (2) three voiceless stops and the affricate /tʃ/; (3) three or four (depending on the dialect) voiceless fricatives; (4) a set of voiced obstruents — /b/, /d/, /ɡ/, and sometimes /ʝ/ —which alternate between approximant and plosive allophones depending on the environment; and (5) a phonemic distinction between the " tapped " and " trilled " r -sounds (single ⟨ r ⟩ and double ⟨ rr ⟩ in orthography).

In the following table of consonant phonemes, /ʎ/ is marked with an asterisk (*) to indicate that it is preserved only in some dialects. In most dialects it has been merged with /ʝ/ in the merger called yeísmo. Similarly, /θ/ is also marked with an asterisk to indicate that most dialects do not distinguish it from /s/ (see seseo), although this is not a true merger but an outcome of different evolution of sibilants in Southern Spain.

The phoneme /ʃ/ is in parentheses () to indicate that it appears only in loanwords. Each of the voiced obstruent phonemes /b/, /d/, /ʝ/, and /ɡ/ appears to the right of a pair of voiceless phonemes, to indicate that, while the voiceless phonemes maintain a phonemic contrast between plosive (or affricate) and fricative, the voiced ones alternate allophonically (i.e. without phonemic contrast) between plosive and approximant pronunciations.