Path planning of unmanned aerial vehicle (UAV) targets at finding an optimal and collision free path in a cluttered environment while taking into account the geometric, physical and temporal constraints. The goal is to reach fully autonomous UAVs robust enough to work in every possible situation and under every possible source of uncertainty. The scientific community is increasingly focusing on this topic and a lot of works has been done in the last decades. It is important to try to go ahead in the research to understand what is the state of the art in order to locate which are the steps to be done to move forward.