Precipitation of nanoparticles from a supersaturated solid solution is important in understanding and controlling the formation of nanostructure, and as a result, many physical properties of materials, such as conductivity, mechanical, thermoelectric, and magnetic behavior of materials. In each case, the precipitation state, including size, density, chemical composition, spatial distribution, particle morphology, and volume fraction, of nanoparticles can all influence the properties of interest. In an effort to design nano/microstructures in steels, mainly for automotive applications, it is important to be able to describe the time evolution of the precipitation state, including both the nucleation and the growth processes. The present review is thus concerned with the homogenous precipitation of carbo-nitride nanoparticles in α-ferrite. The interfacial process, the time evolution of both carbon and nitrogen into precipitates, and the effects of supersaturation and spatial distribution are discussed and clarified. The involved mechanisms are discussed from a theoretical point of view; some major results are illustrated from newly developed experimental methods, and their relevance to topics of current interest is examined. At last, some major outstanding issues have been identified and avenues for further research suggested.