Analog-to-Digital Converter (ADC) is the bridge connecting the analog world and the digital world. With the development of circuit techniques and manufacturing process, its performance indicators have made great progress. The classification and performance characteristics of ADCs are firstly introduced, and then a description is made on the basic principles and technological development of ADCs of different structures including directions: high-speed and high-resolution ADCs. For high-speed ADCs, this article focuses on performance optimization techniques for SAR ADCs and Pipelined-SAR ADCs, such as CDAC controlling methods and comparator design, non-binary redundancy, loop-unrolled, and inter-stage redundancy. For high-resolution ADCs, the various types of Delta-Sigma ADCs and their advantages are analyzed, and the technical characteristics of Zoom ADCs and NS-SAR ADCs introduced. Some new types of hybrid-architecture ADCs are also summarized, describing their composition and research progress.