In this thesis I explored polarimetric properties of cometary dust by focusing on both theory and observations. In the first part, I focused my attention on theoretical modelling of cometary dust particles on microscopic level for the purposes of determining their full light scattering properties. This was aimed at improving the connection between theoretical and laboratory analysis of cometary dust and remote observations of its light scattering properties. I constructed my own aggregate particle creation method and used an existing sophisticated light scattering code that deals with such input. I ran a small-scale parameter survey to analyse trends in polarimetric properties and showed that particle shape and fluffiness will affect the polarimetric response. In the second part, I focused on observations of near-Sun comets; a group that has so far almost never been analysed polarimetrically. I developed a new pipeline for analysis of polarimetric images of comets taken by coronagraphs on board the Solar Terrestrial Relations Observatory spacecraft. I tested the pipeline against a previous analysis of comet C/2011 W3 (Lovejoy), then used it to analyse seven more Kreutz family comets and comet 96P/Machholz. While the latter showed behaviour consistent with a majority of analysed comets, the Kreutz family comets show polarimetric behaviour remarkably different from that of any other comets observed so far. Theories explaining the unusual behaviour are discussed in this work. I have thus significantly expanded our knowledge on Kreutz family comets. In the third and final part, I analysed polarimetric observations of comet 67P/Churyumov-Gerasimenko taken with the Very Large Telescope in parallel with the pre-perihelion phase of the Rosetta mission in 2016. Several jet structures were observed in the coma. Results agree with the expected behaviour of cometary dust in the coma, but tail shows a decrease in polarisation with cometocentric distance, which is unusual.