The NZF domain (Npl4 zinc finger) is a compact zinc-binding module found in many proteins that function in ubiquitin-dependent processes. Present in more than 100 proteins, NZF domains conform to the consensus sequence: x(4)-W-x-C-x(2)-C-x(3)-N-x(6)-C-x(2)-C-x(5), with many more proteins containing recognizable variants of the NZF motif. Consisting of ~35 amino acids, the NZF domain forms a compact module composed of four antiparallel beta-strands linked by three ordered loops and organized about a rubredoxin-like Zn(Cys)4 metal-binding site. While many NZF domains have shown to bind mono- and polyubiquitin, not all NZF domains appear capable of binding ubiquitin.