A single-shot Mueller matrix polarimeter (1700), MMP, comprising: a polarization state generator (1706), PSG, arranged to receive a source optical field (1704) and provide a probe field (1708) having a plurality of spatial portions, each portion having a different polarization state; a polarization state analyser (1718), PSA, arranged to receive a modified probe field (1716) resulting from interaction of the probe field generated by the PSG with a sample under investigation, and further arranged to apply, to each of a corresponding plurality of spatial portions of the modified probe field, a plurality of retardances and a plurality of fast axis orientations; and a detector (1720) arranged to detect an output (1722) of the PSA.