A brief review is given of the continuous metal–nonmetal transition observed in different fluid systems, with special emphasis on recent work by the author and his colleagues. Selected results of abroad experimental survey of the electrical and magnetic properties of fluid binary semiconducting alloys, expanded fluid metals, and fluid selenium are reported. The results are discussed with special emphasis on their relationship to some theoretical areas of controversy, especially the importance of the amount of covalency and ionicity for the electrical and magnetic properties of semiconducting alloys, the role of chemical bond satisfaction in covalent selenium and tellurium for the temperature-induced nonmetal to metal transition, and some speculations concerning the importance of fluctuations and microscopic inhomogeneity for the metal–nonmetal transition in expanded fluid metals. It is concluded that no theory of the metal–nonmetal transition is available which is generally valid for all the fluid systems discussed. It is proposed that measurements of the structure factor and of thermodynamic data of the fluids are necessary to make it possible to formulate a theory which is tested experimentally. The first new results of the structure factor and the compressibility of fluid expanded rubidium are reported.