Korean features a three-way contrast among voiceless stops: aspirated, tense, and lenis. Previous studies have shown that young Seoul Korean speakers produce vowels after aspirated and tense onsets with a higher pitch than those after a lenis onset and that the contrast in Voice Onset Time (VOT) between aspirated and lenis merges. This trade-off between VOT and pitch is suggested as an example of tonogenesis, in which an atonal language develops a tonal contrast. By examining 141 Seoul Korean speakers, this dissertation aims to provide a complete picture of the pitch contrast development and the intonation change, from their initial stage to completion. The findings of this dissertation indicate that all syllables in an Accentual Phrase (AP) starting with a high-inducing consonant is produced with higher pitch values than those in an AP starting with a low-inducing consonant. Furthermore, the results show that females born in the 1950s are the ones who initiated this change, which has almost reached completion in the speech of speakers born in the 1990s. By comparing other languages that underwent tonogenesis, I argue that tonogenesis can affect not only syllables but also large prosodic units and the end result of tonogenesis varies depending on languages’ phonological and morphological characteristics.