In this project, a study will be carried out of the main characteristics that HAPs systems currently have, the main developments, regularizations, applications and the future of these pseudo satellites. In the first section, we will introduce the HAPs concept and briefly explain the different types of HAPs that we can find and enumerate some projects that are actives. Once the concept of HAPs has been introduced, we are going to enumerate the limitations that we must consider when performing HAPs platform deployments, the limitations we find are in the area of telecommunications and in the area of aeronautics. Next, we are going to list the possible scenarios where the HAPs technology could be deployed, at the user level and at gateway level, and some possible scenarios in the future. Next, the technical aspects required for the proper functioning of the HAPs links will be listed the antennas used, the difficulties that we will find in the transmission channel, the source of energy that we will use, ... We will mention the applications that HAPs platforms can offer us and their current state. We will introduce HAPs applications for broadband services, also mentioning possible future 3D, using drones, and 5G applications. We will also explain the use of HAPs for Earth observation and remote sensing applications. Finally, we will enumerate the advantages and disadvantages that we would obtain with the implementation of HAP systems today, mentioning the WRC-19 meeting that will be held from October 28, which can significantly influence the future of HAPs. We will also make a small introduction of the market in HAPs systems.