The book collection has grown and shrank, grown and shrank. Years ago I had nearly sixty Gettysburg related titles alone, but more recently I decided to dedicate more focus on the Western Theater, so many of my Eastern Theater books were moved out. I have looked to keep one definitive account for most of the eastern battles. I have found that I do have spells of mass purchasing, and then spells of thinning the herd so to speak. I have purchased some real dogs of books (mostly self-published) that I do not hesitate to remove from my collection once I realize their value as being valueless.
The organization of my books probably needs a bit of reorganizing, but I sort my shelves into various categories. First there are reference books, those catch all titles that contain information ranging from weapons to collections such as Battles and Leaders. A small naval grouping comes next, and then we have state related books, in alphabetical order by state, which includes regimental and unit histories as well as books that are state specific. Then come the theaters and their related battles and campaigns, Eastern, Trans-Miss, and Western, each in order of occurrence. Lastly I have bios, an area that I have expanded a bit in recent years. And while my collection is definitely Union centric, I have increased the number of Confederate themed books with my research into John H. Morgan's First and Last Kentucky Raids.
Authors that grace the shelves repeatedly are David Powell and Tim Smith, while Perryville, Chickamauga, Antietam, and Gettysburg still have the largest number of battle/campaign titles.
One thing, there are at least a dozen books not on the shelves as I always have a few in the den for whatever the latest writing or research project might be, and there are a half dozen on the nightstand at any one time. I bounce back and forth between titles a lot, mostly staying within the Civil War, but also with my third passion, the Great War (my second passion is Ohio's Indian Wars of the 1790s).