What is in the "Public Domain?
For the purposes of MobileRead, only works where the author has been dead for 70 or more years are in the public domain. Currently (in 2020), that's works where the author (and translator or illustrator if applicable) died before 1950. The rest of this post is written assuming it's still 2020 when you read this.
As you might expect, the legal definition is somewhat complicated, and it depends on where you are in the world - different countries have different copyright lengths.
In most of the world things enter the public domain (PD) a certain number of years after the death of the author. In most countries that number is 70 years, in a few (eg Canada) it's 50. That means all works of authors who died prior to 1950 are PD in Europe; but all works of authors who died prior to 1970 are PD in Canada.
In the US, the rules are rather more complicated, but assuming the work was first published with a valid copyright notice in the US:
- Anything published more than 95 years before the present is PD (i.e. before 1925)
- Anything published before 1964 for which copyright was NOT specifically renewed, is PD.
The net result of this is that some stuff is in the PD in the US, but not elsewhere (early works of authors who had LONG lives - eg Agatha Christie), and a LOT of stuff is PD outside the US but not in the US (works of authors published after 1924 who died before 1950/1970).
As you might expect, there are edge cases where the rules are not clear-cut. E.g. works that weren't published during the author's lifetime.