Research for this thesis was initiated by an interest in the Johannine teaching about the Spirit and the conviction that a fresh understanding of the third person of the Trinity was essential if the Christian Church were to make an adequate contribution to the second half of this century. Study of the New Testament evidence revealed not only the contrast between Johannine and Pauline preoccupation with the Spirit and the paucity of reference to it in the Synoptic Gospels, but also the dearth of recent scholarship in this field. A survey of the Old Testament usage of ךוח as background brought to light the connotation of power which clings to the Spirit of God concept, serving as a reminder that 'spirit' in Jewish thought was functional and dynamic. It is commonly recognized that, while in the Old Testament ךוח is on a higher plane than שפנ, in Greek thought ψυχή is more important than πνεΰμα which is a substantial concept. T. W. Manson has shown in a succinct statement the degree to which our contemporary thought-world reflects the latter emphasis: "We say 'psychic', 'psychology', but keep 'pneumatic' for things like bicycle tires”. Under the guidance of my supervisor Principal Matthew Black of St. Mary's College, The University of St Andrews, my interest was channelled into the richly diverse meanings of ךוח in the Hebrew language and tradition, particularly in the relatively unknown inter-Testamental period. At his suggestion, my attention was concentrated on the Dead Sea texts and this thesis became an attempt to clarify the various ways in which ךוח was used by the Community that produced them. The already famous two-spirit passage of 1QS 3:13 - 4:26 was the obvious starting-point.