This dissertation explores experimentally the properties of the Greek Negative Polarity Items (NPIs) and aims to shed light from different angles to the nature of NPI-hood. The first aspect we explore is the relation between NPI and prosody: based on Veloudis (1982) and Giannakidou (1998 et seq) we explore the distinction between emphatic and non-emphatic NPIs and analyze their relation to scalarity (Giannakidou and Yoon, 2016). In a production study we show that this distinction corresponds to a psycholinguistic reality and that intonation interacts with scalar reasoning. We continue our investigation by looking at the scope properties of the Greek emphatic NPIs. We present a perception study conducted on a group of 6-years-olds native speakers of Greek and show that the emphatic NPIs always take wide scope above negation (Giannakidou, 1998). This result gives us a different insight both on the relation between scope and prosody and to the possibility of prosodic prominence being an intrinsic property of the emphatic class. Finally, we explore two different modes of NPI licensing, semantic licensing vs. pragmatic licensing and through and Acceptability Judgment Task we see that participants’ treat each mode differently. Overall, the present thesis contributes to our understanding of the NPI-hood by presenting an experimental investigation on different aspects of the Greek NPIs.