Augmented reality (AR) has the ability to enhance the real world by using computer-generated information that is projected onto the user's virtual environment. Users can visualise the superimposed information with a selection of display technologies and can interact with it in a natural manner by employing software interfaces, physical markers and hardware interaction devices. AR technology is developing rapidly, but it is still in its infancy. Up to now, only a small proportion of experimental systems address an effective visualisation and interaction interface that can handle different types of multimedia content into a single environment. This thesis presents augmented reality interfaces for visualising and interacting with virtual information in indoor environments. I propose the use of AR techniques to construct innovative applications and demonstrate examples from heritage to learning systems, using an experimental framework developed in this research. A novel AR architecture based on this framework is presented that provides generic solutions to the tasks involved in augmenting different types of digital information and processing of tracking data for natural interaction. Participants within the system can experience a real-time mixture of 3D objects, static video, images, textual information and 3D sound with the real environment. An interactive and user-friendly AR interface was further developed to achieve maximum interaction using simple but effective forms of collaboration. The novelty of the system is that users can browse and select 3D digital information over the internet and superimpose it on an interactive AR environment.