本文主要是探討漢語短語及詞彙層次的輕聲現象。關於短語性的輕聲，鄭良偉先生(1989)是從句法的觀點來分析，本文則採用韻律体系理論來探討。我們提議了一組焦點詞語的原則及幾個相關的制約。此外，我們從蕭宇超先生(1991 & 1994)的韻板計數理論來觀察輕聲的節奏問題，因而修訂了虛詞音板指派及音板連接方向的原則，也建議了一條抵輔音板加入的規則。 This thesis deals with neutral tone sandhi in Mandarin Chinese at the phrasal and lexical levels. Previous research of the phrasal neutral tone, e.g., R. Cheng (1989), has focused only at the syntactic level. In this research, we employ prosodic theories (Selkirk (1984 & 1986), Nespor and Vogel (1986), etc.) to condition phrasal neutral tone sandhi, and propose a set of focal phrasing principles and a couple of relevant constraints. In addition, we discuss the rhythm of neutral tone under the framework of the beat-counting theory (Hsiao, 1991 & 1994) to see in what ways the theory has to be modified. We propose a pair of revised principles of functor beat assignment and directional beat adjunction, along with a backup rule of the default beat addition.