The international meeting "Understanding Relativistic Jets" is a follow up of our previous Krakow meetings focused on the physics of astrophysical jets in AGN and in the Galactic sources (e.g., "Challenges of Relativistic Jet" 2006), but also on the related issue of particle acceleration in astrophysical plasma (e.g., "Particle Acceleration in Astrophysical Objects" 2003).

This time, however, in addition to summarizing the recent progress in the field, we also plan to celebrate the 65th birthday of Prof. Marek Sikora, who contributed significantly to the understanding of relativistic jets and AGN phenomena in general. Irrespective of this special context of the gathering, however, our meeting is a regular international conference. It aimes to summarize and to discuss recent progress in understanding astrophysical jets.