Augmented Reality is a technology based on image processing and computer graphics employed to merge a real world with virtual images. The system provides the user a real-time video feed with overlapped information generated by a computer based system taking into account the content of the video, the location and orientation of the user. This Master Thesis provides the background information and state of the art of AR systems. It focuses on the system composition and the difficulties found in their implementation. Especially, the issues arised while aligning the real world images with the virtualized ones. Such problem becomes a key factor to achieve the user immersive experience. MonDecor application is presented as indoor room design application to select furniture from a manufacturer/reseller catalogue. The application requires to configure a virtual environment to be represented in an empty room as AR system. This application, then, becomes a perfect platform to present the problems of registering and tracking the location of virtual 3D objects observed in a mobile device based AR system. The application requires to take into account the environment, the user location/orientation and visual aids to deploy a furnish virtual room and merge it with the real world. Results obtained from the implementation of both techniques, Marker and Markerless based AR methods, are presented as potential solutions for applications currently developed in different customer environments. Marker based AR method employs markers represented by images that, when is recognized by the system it displays a virtual object 3D overlapped with the real world creating a mixed reality. Markerless based AR method uses inertial sensors embedded in the mobile device to determine the direction and the angle of the device movement. Therefore, the system knows where to overlap the 3D objects in real world.