An overview of the soft X-ray polarimetry udertaken at BESSY over the last 10 years is presented. At BESSY

ten elliptical undulator beamlines are operating in the VUV and soft X-ray range

which enables the polarisation state of the synchrotron radiation to be changed from linear (horizontal or vertical) to left- or right-handed circular. It is essential that the degree of polarisation is known quantitatively

since this is a normalization quantity for many polarisation-sensitive experiments (

e.g.

MCD-spectroscopy). For a polarimetry experiment i.e. the measurement of the polarisation state of light

two optical elements are required acting as a phase retarder and a linear polariser

respectively. In the soft X-ray range

specially tailored multilayers (ML) operating in transmission and in reflection have been developed and optimized for this purpose. By matching the ML-parameters (period

thickness ratio) to an absorption edge of one of the constituent materials

a resonantly enhanced polarisation sensitivity can be achieved. Thus

ML-polarimetry is strongly connected with At-Wavelength Metrology of these polarisation optical elements

for which the instrumentation and results are presented.Examples of magneto-optical spectroscopy and polarimetry to determine properties of magnetic thin films or optically active substances are also presented (Faraday and Kerr effect

L-MOKE).