Edit: I wrote this while the previous answer was being posted!
No, they are books that contain lots of texts from several authors, a compilation for learning purposes mostly. I bet there is a term in english. Maybe readers? So, they can be from any publishing house, and for several levels, beginner etc.
Studying them produced great results, but we did have teachers to help. But if you have experience with languages of course you can do it alone, especially since they provide vocabulary and grammar/syntax notes. They are not textbooks, but they have worked for me so I thought I'd share.
Here is a favourite of mine (and of many students). I have the 17th edition, this seems to be the 9th. A classic! There are others, more recent ones if you search around.
Πολλ' οίδ' ἀλώπηξ, ἐχῖνος δέ έν, μέγα.