If you are interested in crossbows in particular or in archery, I recommend "Iolo's First Book of Crossbows" by Master Iolo of Ansteorra. This recently completed work is an excellent general source of information on crossbows or buying a period style crossbow. It has good advice on improving the performance of the crossbow you now have or increasing your own skill in shooting.
The first part covers the component parts of the crossbow and how they work. It explains the variations among the same parts.
Next is a section on the development of the crossbow, from Roman times to the bullet bows which were popular until the early 1800's.
The next two chapters cover differences in the appearance of the crossbow by region and date. This is useful for anyone wishing to match a crossbow to their persona.
The section on `Getting what you want' provides helpful information on deciding what type of crossbow you should get based on your needs: target, combat or display.
The following sections cover setting up and tuning your bow and bolts to get maximum accuracy and provides advice on shooting technique.
The chapter `When things go wrong' explains the mechanical problems that can arise with a crossbow, how to determine the problem and how to correct it.
The book is put together well and nicely printed. Its fifty pages are full of informative diagrams and illustrations, several per page. It is definitely a worthwhile addition to any archer's library.
The author, David Watson, better known in the SCA as Master Iolo, is proprietor of New World Arbalest and craftsman of fine medieval and renaissance crossbows.
You may order the book from: David R. Watson, 201 W. Crestland Dr., Austin TX 78752. (512) 453-2628. Cost is $8.00 plus $2.00 shipping and handing.