Who or What determines that a book is a classic?

Time. Good writing. Popularity.

Combined, they make a book "classic."

Books "thought poorly of" are not classics because of that.

Any book in that category, now called classic, is judged so by the fact the book is read in spite of any judgment via "controversy."

ADD: Must disagree with answer that 'writers and critics' are what makes books classics. Readers do, and time.

2nd ADD: I think this is not needed; you already know...

"...dead authors," "books before copyright" are NOT what makes work classic.

To "hear about" a book is of great necessity to make it classic.

A book "popular" when written is not classic until 'Time' passes and it remains popular; that answerer probably knows it.

3rd ADD: Caught a glimpse of your addition.

The primary reasons books become classics are time and continued reading.

There is no way to judge a current book as 'classic' without the passage of time and continued reading. We can't know what will happen in the future.

It's mostly the readers of the time. But the critics and other writers themselves also get a say. No one really decides officially.

I think that books like Harry Potter will become the classics of our age.

To tell the truth, I don't know about Rainbow 6 vs RBOG( Red Badge of Courage). I guess it's because they have stood the test of time and people throughout time have acknowledged them as the "classics". Rainbow 6 and others will have their chance.

Over time, societal norms change, so I guess those books were remembered and became widely read. Maybe a new generation read them simply because their parents forbade the book, then thought Hey, this is actually really good book.

The "educated" populace decides a book's classic status.

Many classics were popular during their time, too.

It's a consensus, mostly, of writers and critics. A book is considered a classic essentially because enough people with a significant knowledge of literature believe it is a classic.

Okay, please forgive me, but this really is my personal definition of a classic book and I just answered this question for someone else awhile ago, so I'm going to copy that answer here.

' I think that a classic is a book which is clearly of its time but which expresses universals of the human experience in such a way that it remains vital and pertinent throughout the span of time. '

i guess a classic is a book that was written before the whole copyright law came out. so the author has no real claim on them ( and the author would be dead i guess... or really really old) so whether they were good or not they're still "classics" and you can read those books online for free. and alot of books are classics... not just the famous ones by charles dickens, mark twain, jane austen and other famous writers. there are books that you never heard of that are considered classics.

I think it is determined if the book has withstood the test of time, and even though it was made a long time ago, it is still read or well-known.