Owned and missing
See your progress by title. Owning two copies of the same book does not fill a different gap in the series.
See the titles you own and the ones you still need. A supported series guide gives you a useful list to take on your next bookshop visit.
Download on the App Store
See your progress by title. Owning two copies of the same book does not fill a different gap in the series.
Look through all the titles, just the missing ones, or the next book to find.
Save a wanted book separately from your collection. Add your copy when you find it.

A recommendation from a friend, a particular hardcover, the next book in a series. Keep those wanted books together.
Series coverage and ordering depend on available guides and catalog data.