This book covers both historical and contemporary issues, from the need for coat armour in mediaeval warfare to modern air-force insignia.
It doesn't spend a lot of space on blazon: just enough to get you started. But it does include right up-to-the-minute information about many countries and subfields, from Scandanavia to Japan, and from medical heraldry to armour.
My only criticism: it is very light on coverage of Scotland, which is arguably the country with the best developed and most enforced heraldic code in the world.