In this short course I will present and discuss the observational properties and some theoretical implications of astrophysical jets (in particular AGN jets) as revealed by their polarised emission, throughout the EM spectrum. The course will start with a brief discussion of the observational techniques and how to interpret the polarisation information, and will proceed with a review of the current status of our knowledge regarding a polarimetric view of jets. I will focus on the discussion of some key physical parameters and measurements that can be extracted from the polarimetric data, and the physical insights they provide. Finally, I will discuss some theoretical aspects which can be tested or probed with polarimetric measurements. To conclude, I will give some personal views (criticisms and proposals) on the use of polarimetric data in combination with multi-band light-curves and SEDs to probe the physics of AGNs, and specially blazars.