Mixed reality (MR), sometimes referred to as hybrid reality,^[1] is the merging of real and virtual worlds to produce new environments and visualizations where physical and digital objects co-exist and interact in real time. Mixed reality takes place not only in the physical world or the virtual world,^[1] but is a mix of reality and virtual reality, encompassing both augmented reality and augmented virtuality^[2] via immersive technology. The first immersive mixed reality system, providing enveloping sight, sound, and touch was the Virtual Fixtures platform developed at the U.S. Air Force's Armstrong Laboratories in the early 1990s.

In 1994 Paul Milgram and Fumio Kishino defined a mixed reality as "...anywhere between the extrema of the virtuality continuum" (VC),^[2] where the virtuality continuum extends from the completely real through to the completely virtual environment with augmented reality and augmented virtuality ranging between. The first fully immersive mixed reality system was the Virtual Fixtures platform developed at US Air Force, Armstrong Labs in 1992 to enable human users to control robots in real-world environments that included real physical objects and 3D virtual overlays called "fixtures" that were added enhance human performance of manipulation tasks. Published studies showed that by introducing virtual objects into the real world, significant performance increases could be achieved by human operators.^[4][5]

The continuum of mixed reality is one of the two axes in Steve Mann's concept of mediated reality as implemented by various welding helmets and wearable computers and wearable photographic systems he created in the 1970s and early 1980s,^{[6][7][8][9][10]} the second axis being the mediality continuum, which includes, for example, Diminished Reality (as implemented in a welding helmet or eyeglasses that can block out advertising or replace real-world ads with useful information)^[11]

"The conventionally held view of a Virtual Reality (VR) environment is one in which the participant-observer is totally immersed in, and able to interact with, a completely synthetic world. Such a world may mimic the properties of some real-world environments, either existing or fictional; however, it can also exceed the bounds of physical reality by creating a world in which the physical laws ordinarily governing space, time, mechanics, material properties, etc. no longer hold. What may be overlooked in this view, however, is that the VR label is also frequently used in association with a variety of other environments, to which total immersion and complete synthesis do not necessarily pertain, but which fall somewhere along a virtuality continuum. In this paper we focus on a particular subclass of VR related technologies that involve the merging of real and virtual worlds, which we refer to generically as Mixed Reality (MR)."

In a physics context, the term "interreality system"^[12] refers to a virtual reality system coupled to its real-world counterpart. A paper in the May 2007 issue of Physical Review E^[13] describes an interreality system comprising a real physical pendulum coupled to a pendulum that only exists in virtual reality. This system apparently has two stable states of motion: a "Dual Reality" state in which the motion of the two pendula are uncorrelated and a "Mixed Reality" state in which the pendula exhibit stable phase-locked motion which is highly correlated. The use of the terms "mixed reality" and "interreality" in the context of physics is clearly defined but may be slightly different from in other fields.

Augmented virtuality (AV), is a subcategory of mixed reality which refers to the merging of real world objects into virtual worlds.^[15]

As an intermediate case in the virtuality continuum, it refers to predominantly virtual spaces, where physical elements, e.g. physical objects or people, are dynamically integrated into, and can interact with, the virtual world in real time. This integration is achieved with the use of various techniques. Often streaming video from physical spaces (e.g., via webcam)^[16] or using 3-dimensional digitalisation of physical objects.^[17]

The use of real-world sensor information (e.g., gyroscopes) to control a virtual environment is an additional form of augmented virtuality, in which external inputs provide context for the virtual view.

A topic of much research, MR has found its way into a number of applications, evident in the arts and entertainment industries. However, MR is also branching out into the business, manufacturing and education worlds with systems such as these:

• IPCM – Interactive Product Content Management

Moving from static product catalogs to interactive 3D smart digital replicas. Solution consists of application software products with scalable license model.

• SBL – Simulation Based Learning

Moving from e-learning to s-learning—state of the art in knowledge transfer for education. Simulation/VR based training, interactive experiential learning. Software and display solutions with scalable licensed curriculum development model.

• Military Training

Combat reality is simulated and represented in complex layered data through HMD.

• Real Asset Virtualization Environment (RAVE)

3D Models of Manufacturing Assets (for example process manufacturing machinery) are incorporated into a virtual environment and then linked to real-time data associated with that asset. Avatars allow for multidisciplinary collaboration and decision making based on the data presented in the virtual environment. This example of Mixed Reality was pioneered and demonstrated by Kevyn Renner of Chevron Corporation for which a United States Patent 8,589,809, B2 "Methods and Systems for Conducting a Meeting in a Virtual Environment" was granted November 19, 2013.^[18] One of the earliest patents describing mixed reality is shown by Michael DeLuca in United States Patent 6,064,354 "Stereoscopic user interface method and apparatus" granted May 16, 2000.^[19]

• Remote working

Mixed reality allows a global workforce of remote teams to work together and tackle an organization’s business challenges. No matter where they are physically located, an employee can strap on their headset and noise-canceling headphones and enter a collaborative, immersive virtual environment. Language barriers will become irrelevant as AR applications are able to accurately translate in real time. It also means a more flexible workforce. While many employers still use inflexible models of fixed working time and location, there is evidence that employees are more productive if they have greater autonomy over where, when and how they work. Some employees prefer loud work spaces, others need silence. Some work best in the morning, others at night.Employees also benefit from autonomy in how they work because everyone processes information differently. The classic VAK model for learning styles differentiates Visual, Auditory and Kinesthetic learners.^[20]

• Healthcare

Surgical and ultrasound simulations are used as a training exercise for healthcare professionals. Medical mannequins are brought to life to generate unlimited training scenarios and teach empathy to healthcare professionals.^[21]

• Aviation

Virtual models are used to allowed scientists and engineers to interact with a possible future creation before it touches the factory floor. These models provide the opportunity to gain an intuitive understanding of the exact product, including real size and constructions details that allow a closer inspection of interior parts. These virtual models are also used to find hidden problems and reduce time and money.^[22]

Here are some more commonly used MR display technologies:

• 
  Cave Automatic Virtual Environment
• 
  Head-up display
• 
  Head-mounted display
• 
  Tablet PC
• 
  Computer display
• 
  Personal Digital Assistant
• 
  Mobile phones
• 
  Handheld PC

• Example projects from the Mixed Reality Lab at National University of Singapore / Keio University.
• Examples of Augmented Reality with vision-based positioning system.
• Ars Electronica
• ASTERION VR, Merged Reality for military and Law Enforcement training in Virtual CQB.
• EyeToy
• BAMZOOKi
• FightBox
• Microsoft Hololens
• WebGuyz Mixed Reality Education Platform
• Nokia Point & Find
• Interactive Multimedia Lab A research lab at the National University of Singapore focuses on Multi-modal Mixed Reality interfaces.
• Mixed Reality vs. Mixed Realities
• The Center for Research in Computing and the Arts and Calit2 at UCSD are home to a number of Mixed Reality projects, including Mixed Reality Performances by Micha Cárdenas and Elle Mehrmand
• The Dawn of Mixed Reality An introduction of Mixed Reality and compilation of example projects
• Mixed Reality Environments as Collaborative and Constructive Learning Spaces for Elementary School Children
• zSpace

Media related to Mixed reality at Wikimedia Commons

• Signer, Beat & Curtin, Timothy J. (2017). Tangible Holograms: Towards Mobile Physical Augmentation of Virtual Objects, Technical Report WISE Lab, WISE-2017-01, March 2017.
• Fleischmann, Monika; Strauss, Wolfgang (eds.) (2001). Proceedings of »CAST01//Living in Mixed Realities« Intl. Conf. On Communication of Art, Science and Technology, Fraunhofer IMK 2001, 401. ISSN 1618-1379 (Print), ISSN 1618-1387 (Internet).
• Interactive Multimedia Lab A research lab at the National University of Singapore focuses on Multi-modal Mixed Reality interfaces.
• Mixed Reality Geographical Information System (MRGIS)
• Costanza, E., Kunz, A., and Fjeld, M. 2009. Mixed Reality: A Survey Costanza, E., Kunz, A., and Fjeld, M. 2009. Mixed Reality: A Survey. In Human Machine interaction: Research Results of the MMI Program, D. Lalanne and J. Kohlas (Eds.) LNCS 5440, pp. 47–68.
• H. Regenbrecht and C. Ott and M. Wagner and T. Lum and P. Kohler and W. Wilke and E. Mueller, An Augmented Virtuality Approach to 3D Videoconferencing, Proceedings of The 2nd IEEE and ACM International Symposium on Mixed and Augmented Reality, pp 290-291, 2003
• Kristian Simsarian and Karl-Petter Akesson, Windows on the World: An example of Augmented Virtuality, Interface Sixth International Conference Montpellier, Man-machine interaction, pp 68-71, 1997
• ^[permanent dead link] Mixed Reality Project: experimental applications on Mixed Reality (Augmented Reality, Augmented Virtuality) and Virtual Reality.
• Mixed Reality Scale – Milgram and Kishino’s (1994) Virtuality Continuum paraphrase with examples.
• IEICE Transactions on Information Systems, Vol E77-D, No.12 December 1994 - A taxonomy of mixed reality visual displays - Paul Milgram, Fumio Kishino