微4/3系统（Micro Four Thirds system, MFT，或也简写为M4/3、M43）是由奥林巴斯和松下公司（Panasonic）共同研发、在2008年8月5日发布的新一代可更换镜头相机镜头卡口系统。与4/3系统不同，它取消了传统单反相机中大都会具备的反光镜、五棱镜等结构，使得相机机身变得更加小巧。严格来说，根据狭义的定义由于缺乏反光镜结构，微4/3系统的相机已经不能称为「单镜头反光相机」，而是属于电子式取景可换镜头相机（MILC）的类别。

然而，日本官方方面还是将之与DSLR同样归类于「数字一眼相机」（デジタル一眼）的范畴，主要考量的是其特性与单眼几乎没有差别（除机身厚度与反光镜有无这两点不同之外，举凡光学、感光片幅构造与可换镜头特性都是一样的）。

The Micro Four Thirds system (MFT) is a standard created by Olympus and Panasonic, and announced on August 5, 2008, for the design and development of mirrorless interchangeable lens digital cameras, camcorders and lenses. In 2014, JK Imaging Ltd., which holds the Kodak brand, released its first Micro Four Thirds camera, the Kodak Pixpro S-1; several lenses and niche camera makers have products made for the standard. In 2015, DJI provided its drone with optional MFT cameras. Both cameras can capture 16MP stills and up to 4K/30fps video with an option of 4 interchangeable lenses ranging from 12mm to 17mm.