Various fiber-optic connectors have been developed during the 40 years since optical fiber communications systems were first put into practical use. During the first two decades, as the domain of optical fiber communication systems expanded from trunk lines to subscriber lines and customer premises, the main focus changed from performance improvement to miniaturization and cost reduction. After that, new interconnect technologies were continuously developed to meet new requirements such as high-power transmission, high-density on-board wiring, and multicore fiber interconnection. Despite many improvements, the principle and basic structure of the optical connector have hardly changed. Zirconia ferrules and split sleeves are used for single fiber coupling, MT ferrules are used for multifiber connectors, and both types use physical contact technology. This paper describes the key technologies for fiber-optic connectors, a brief history of optical connector improvements and recent technical issues related to fiber-optic interconnect technologies.