The creator of Esperanto, L. L. Zamenhof, illustrated Esperanto pronunciation by comparing its letters with their equivalents in several major European languages and declaring a principle of "one letter, one sound". Given that the comparison languages were not completely identical, he later advised that the pronunciation of Italian could be considered a model for Esperanto.
With over a century of use, Esperanto has developed a phonological norm, including accepted details of phonetics, phonotactics, and intonation, so that it is now possible to speak of proper Esperanto pronunciation and properly formed words independently of the languages originally used to describe Esperanto. This norm diverges only minimally from the original ideal of "one letter, one sound"; that is, it accepts only minor allophonic variation.
Before Esperanto phonotactics became fixed, foreign words were adopted with spellings that violated the apparent intentions of Zamenhof and the norms that would develop later, such as poŭpo (“poop deck”), ŭato (“Watt”), and matĉo (“sports match”). Many of these coinages have proven to be unstable, and have either fallen out of use or been replaced with pronunciations more in keeping with the developing norms, such as pobo for poŭpo, vato for ŭato, and maĉo for matĉo. On the other hand, the word jida (“Yiddish”), which was also sometimes criticized on phonotactical grounds but had been used by Zamenhof, is well established.
Within a word, stress is on the penultimate syllable, with each vowel defining a syllabic nucleus: familio [fa.mi.ˈli.o] "family". An exception is when the final -o of a nominative singular noun is elided, usually for poetic reasons, as this does not affect the placement of the stress: famili' [fa.mi.ˈli].