Proto-Iranian descends from Proto-Indo-Iranian and Proto-Indo-European. Speakers linked to Andronovo archaeological culture. Four main dialects: Old Northwest, Northeast, Central, Southwest Iranian. Satem language with palatals shifting to sibilants. PIE *p remains p, like pitār ''father''. PIE *s becomes h except before/after certain sounds. Laryngeals vocalized late in Indo-Iranian. PIE *l shifts to r across Iranian languages. Aspirated stops spirantize to f, θ, x in most Iranian tongues. Palatovelars *ḱ, *ǵ become s, z in Avestan and most modern Iranian. Old Persian shows θ, d instead. *cw becomes sp in most Iranian, s in Old Persian. Develops into Old Iranian like Avestan and Old Persian. Avestan close temporally to Proto-Iranian. Many Old Iranian features spread via dialect continuum. Unwritten dialects ancestral to most modern Iranian languages. Examples include aspa ''horse'' from *Hácwah. Haoma ''ephedra'' parallels soma. Brātar ''brother'' from *bráHtā.