That depends on the country.
In Belgium, copyright protection lasts until 70 years after the death of the last surviving author. The protection after the death of the authors is for the benefit of the heirs or their representatives.
On this page you will find a list of the standard term of copyright in other countries.
Anonymous works are protected until 70 years after they are made public.
Posthumous works that have been discovered after the expiry of the term of protection are granted a term of protection of 25 years. This term starts when the work is made public.