From the reviews:
"It consists of five chapters, and all chapters close with a great number of additional explanatory notes connecting the results with a thorough bibliography. ... It contains a rich list of 210 references of carefully selected old and new works, which, also, might be a good source to graduates for further study of the theory of periodic differential operators." (George Karakostas, zbMATH, Vol. 1267, 2013)
"It consists of five chapters, and all chapters close with a great number of additional explanatory notes connecting the results with a thorough bibliography. ... It contains a rich list of 210 references of carefully selected old and new works, which, also, might be a good source to graduates for further study of the theory of periodic differential operators." (George Karakostas, zbMATH, Vol. 1267, 2013)