Medieval Underpants & Other Blunders by Susanne Alleyn
A wonderful little book aimed at writers of historical fiction. This book (I bought the paperback as I thought I'd want to refer to it over and over) tells you of the most common anachronisms to be found in historical fiction, and teaches you how to avoid making the same mistakes.
The basic message is - look it up! Always look it up, even if you think you know. Did Dark Ages Irish peasants eat spuds? No, because potatoes originate in South America so BC (Before Columbus) they were unknown in Europe. What kind of underpants did medieval peasant women wear under their skirts? None. You try peeing in the corner of a field in long skirts, if you've also got to untie your knickers and pull them down.
Having once almost had my 1820s child go to sleep cuddling a teddy bear (which were named after US president Theodore 'Teddy' Roosevelt after he refused to shoot a bear during a hunting trip) I thought I could make good use of this book. You need to be very careful when writing historical fiction - it's not just the obvious anachronisms, but the less obvious ones such as use of colloquialisms and cliches. Your seventeenth century teenager couldn't be accused of going off the rails, for example (refers to train derailments); neither could he get tired and run out of steam (steam engines not invented till 1780s).
As the author says in her book, Wikipedia is your Friend.
This book is a lively and informative read, and is recommended for all those who love history, but especially if you are aiming to write historical fiction.