A phenomenon which has attracted an enormous amount of attention recently is the so-called pro - drop or null subject parameter. In this chapter I examine the null subject construction in Welsh, showing that the null element in this construction is pro, the phonologically null pronominal. Section 1. gives abrief introduction to the issues surrounding the investigation of the null subject parameter. In Section 2. I present the Welsh data, and Section 3. proposes an analysis of the Welsh null subject construction based on the notion of Agreement Context. In Chapter Three I show that this analysis extends straightforwardly to the distribution of pronominal (both pro and overt) arguments in general.