Every luthier and every performer has a personal concept of which sound they want from their instruments. To explain how these ideas can be turned in the design of a classical guitar, this book presents theoretical analysis, guidelines and practical indications. The book is meant for luthiers who feel the need to go beyond their experience, bringing forward their research with no need to forsake their personal touch and creativity. The book is also addressed to guitar players who may find answers about the guitar sound and cast a more competent look on the 'magic' world of lutherie. Although this is not an handbook on guitar construction, some reader will be possibly inspired to build its own guitar, following the designing criteria illustrated here. Finally the book addresses readers with a technical education in Engineering or Physics, curious about how certain basic principles of Acoustics can be applied to the operation of a musical instrument. Mathematical formulations have been reduced to a minimum; readers willing to go deeper on these subjects can refer to the specific publications mentioned in the text