  We obtain unconditional, effective number-field analogues of the three
Mertens' theorems, all with explicit constants and valid for $x\geq 2$. Our
error terms are explicitly bounded in terms of the degree and discriminant of
the number field. To this end, we provide unconditional bounds, with explicit
constants, for the residue of the corresponding Dedekind zeta function at
$s=1$.
