title_body: How to effectively manage ebooks using Calibre? I started using Calibre and I'm unable to decide how to effectively use it to manage my ebooks.
  I've a huge collection of ebooks organized by subject into folders like Political Science, History - World, History - US etc. Till using Calibre, these folders were synced across all of my devices (Android phone, tablet, desktop) using Cloud storage. In this way I could browse any subject anywhere using either browser or file explorer or in android phone.
  
  But when I have added the collection to Calibre, it has destroyed this folder structure and made it one folder per author. If I'm syncing this library using cloud storage, I've no way to know which are History books and which are political science books.
  
  What is the effective way to manage books using calibre?
upvoted_answer: As written in the Calibre manual you should use tags:
  
  
    But suppose you want to find all unread science fiction books. There’s no easy way to do this with this folder scheme, [...] In calibre, you would instead use tags to mark genre and read status and then just use a simple search query like tag:scifi and not tag:read.
  
  
  It might take a while to get everything properly tagged, but after that it will be easy to find what you want.