The Classic FM Pocket Book of Music may be tiny enough to keep in your pocket but it's also stuffed full of facts you always wanted to know about music - not always expressed entirely objectively (e.g. "the bassoon's just like a didgeridoo wearing too much jewellery"). It attacks 125 subjects ranging from Beethoven to film music, and answers some long overdue questions along the way, such as "why are conductors like support tights?". All this in one tiny book: if it had seams, they'd be bursting.
"From Adagio to Zipoli, by way of intermezzo and Tavener, this perfect little book takes all the mystique out of classical music, pulling off the trick of being neither pompous nor patronising" - Stephen Fry