Introduction to Normed *-Algebras and their Representations, 6th ed
  This book treats:   - spectral theory of Banach *-algebras,   - basic representation theory of normed *-algebras,   - spectral theory of representations of commutative *-algebras.   A novel feature of the book is the construction of the enveloping C*-algebra of a general normed *-algebra. 
Marco Thill