In 1997 Manuela de Sa wrote "Segredos da Voz", a book on singing technique published by Sebenta editions. To read some excerpts from her book (in Portuguese), please click this link: http://pt.shvoong.com/authors/manuela-de-sá/ To buy this book, please contact Apolo 70 (bookstore): http://www.livapolo.pt/index.php?action=contactos