Proto-Indo-European (PIE) phonemes included consonants, vowels, resonants, and laryngeals (see Lehmann's book Proto-Indo-European Phonology and other manuals on Indo-European phonology).
Obstruents are stop consonants. In the first table, below, reconstructed PIE obstruents are transcribed using "traditional" rendering.
|Voiceless (no aspiration)||P||T||K||Kw|
|Voiced (no aspiration)||B||D||G||Gw|
* In these tables, palatal and velar obstruents have been collapsed into a single column; distinctions between these types may be indicated elsewhere.
Most handbooks reflect the traditional view re: obstruents, above. An alternative view, labelled Glottalic Theory, is reflected in the second table, below, whose contents define one-to-one replacements of the reconstructions in the "traditional" table, though they constitute different views re: the sounds actually used to speak PIE.
|Voiceless (aspiration optional)||P(h)||T(h)||K(h)||Kw(h)|
|Voiced (aspiration optional)||B(h)||D(h)||G(h)||Gw(h)|
According to Glottalic Theory, for example, the PIE language was not spoken using the "traditional" (but rare) phoneme /b/; rather, it was spoken using the glottalic (but rare) phoneme /p'/. For more on the Glottalic Theory, see the section on phonology in Thomas V. Gamkrelidze & Vjaceslav V. Ivanov, Indo-European and the Indo-Europeans (1984 Russian original translated by Johanna Nichols; Berlin: de Gruyter, 1995, 2 vol's); a topical summary by Allan Bomhard appears in the Glottalic Theory section of our Reconstructing PIE Phonology page.