Record of American Uniform and Historical Buttons - Bicentennial Edition by Alphaeus H. Albert. I don't think any study of military buttons can be undertaken without taking in Albert's book. Whether you are a collector, historian, re-enactor, etc. this book makes a great addition to any historical library. If you plan on buying any original buttons you will most likely encounter the numbering system set forth by Albert so it's a good idea to start here.