A focus metrology target includes one or more periodic arrays of features. A measurement of focus performance of a lithographic apparatus is based at least in part on diffraction signals obtained from the focus metrology target. Each periodic array of features includes a repeating arrangement of first zones interleaved with second zones, a feature density being different in the first zones and the second zones. Each first zone includes a repeating arrangement of first features. A minimum dimension of each first feature is close to but not less than a resolution limit of the printing by the lithographic apparatus, so as to comply with a design rule in a given a process environment. A region of high feature density may further include a repeating arrangement of larger features.