This paper presents an overview of augmented reality, starting from its conception, passing through its main applications, and providing essential information. Part of the article is dedicated to hardware and software components used in AR systems. The last part of the paper highlights the limitations related to the design of these systems, the shortcomings in this area, and the possible future fields of application of this technological innovation.

Although the definitions of AR, mixed reality, and VR date back to 1992, the application and study of these technologies can already be found in the late 1950s. Huge steps have been made every year to develop new AR technologies: clear examples of that are all the things considered science fiction that are now possible through new technologies such as AR and VR. However, there is a substantial difference between VR and AR: the former replaces the natural environment with the digital one, projecting the user into this simulated environment using a computer; the latter, on the other hand, projects digital objects into the natural environment using head-up devices, AR glasses, or commonly used devices such as smartphones or tablets, thus adding virtual information to the actual space. 

The article showcases the main AR applications to games, helath sector, school, business, museums, etc and after that introduces the topic of AR systems, which leads to industry applications. AR is considered as one of the pillars of the new industrial revolution envisaged by Industry 4.0. However, the current limitations of this technology are not particularly contemplated in the literature, especially in the case of its introduction into a natural work environment, where daily activities could be carried out by operators using AR-based approaches. The article concludes that, even though the sector is booming, much still needs to be improved and adapted for the widespread use of AR in Industry 4.0.