This is the first complete study of Semitic internal noun patterns since that of Jacob Barth, over a century ago. Drawing on the earlier work of Semitists and linguists, this work presents a comprehensive new synthesis. This diachronic-comparative study presents the internal patterns individually and organizes them systematically. This study investigates the special role of noun patterns in isolated nouns and gives a complete list of reconstructible isolated nouns. This diachronic-comparative study presents the internal patterns individually and organizes them systematically. The roles of the patterns in the derivation of nouns from roots, and in nominal inflection, are shown as part of a reconstructed system. This study investigates the special role of noun patterns in isolated nouns, and gives a complete list of reconstructible isolated nouns. The heart of the book is devoted to studies of all individual reconstructible internal patterns with their Semitic reflexes, including mono- and bisyllabics and patterns with ungeminated or geminated second or third consonants. The book reaches conclusions on the structure of the Proto-Semitic pattern system, including categories of reconstructible and non-reconstructible patterns, semantic groups of patterns, and relationships between different patterns. Further, patterns merge and split diachronically, appearing in different roles in the attested languages, where new pattern systems are formed.