Traditionally SLR and DSLR camera design has incorporated a mirror and prism system for viewing a through-the-lens image in the camera's viewfinder of the scene being photographed. Effective as this system is, it has constrained the development of more compact digital cameras with interchangeable lenses, due to the size of the mirror and prism assembly.
Since the introduction of Live View in Digital SLR cameras, where the scene can be previewed on the camera's LCD screen – much like a compact digital camera - manufacturer's have subsequently been able to develop cameras that no longer require the mirror and prism-style system. Thus they have been able to create Compact System Cameras (CSC) with interchangeable lenses - sometimes with electronic viewfinders - in a very small form factor.
Panasonic were the first to develop these mirrorless interchangeable lens compacts in the shape of the G Series Micro 4/3 cameras, with Olympus following suit shortly after with their PEN Micro Four Thirds system. Since then Ricoh has developed the GXR system, Samsung released their NX series of micro system cameras, and Sony introduced their popular NEX mirrorless cameras using the new Sony E-mount system.
With a growing list of compatible lenses - and many OEM and third-party lens adapters available that allow a huge range of lenses to be used - the Compact System Camera (CSC) category is constantly evolving, giving users who demand a very small and portable camera system that delivers high quality DSLR-like images, without the bulk of a DSLR, a fantastic range of options.