I think it depends a lot on the language. Some languages are very stable and backward-compatible, like Perl, tcl or common lisp. Old books would be very helpful

I think it depends a lot on the language. Some languages are very stable and backward-compatible, like Perl, tcl or common lisp. Old books would be very helpful for them. Other languages, like Python, change a lot with a couple releases, so old books would not be very helpful. As others reminded, some books are timeless, because they deal with the fundamentals of programming, not specific languages.