In this chapter we present a brief summary of methods, instruments and calibration techniques used in modern astronomical polarimetry in the optical wavelengths. We describe the properties of various polarisation devices and detectors used for optical broadband, imaging and spectropolarimetry, and discuss their advantages and disadvantages. The necessity of a proper calibration of the raw polarisation data is emphasised and methods of the determination and subtraction of instrumental polarisation are considered. We also present a few examples of high-precision measurements of optical polarisation of black hole X-ray binaries and massive binary stars made with our DiPol-2 polarimeter, which allowed us to constrain the sources of optical emission in black hole X-ray binaries and measure orbital parameters of massive stellar binaries.