A numerical microphysical model that treats one-dimensional vertical transport of sulfuric acid/water solution aerosols, their nucleation, growth/evaporation, coagulation, and sedimentation, is applied to the condensational middle and lower Venus clouds. The model predicts the vertical profiles of sulfuric acid gas and water vapor, cloud microphysical properties, and the acid concentration of the aerosol particles. Results of model simulations agree favorably with Pioneer Venus particle size spectrometer data, extinction and backscattering coefficients measured by Pioneer Venus and Venera probes,in situand remote observations of cloud optical depth, and sulfuric acid vapor abundances retrieved from Magellan radio occultation data. It is found that the lower Venus cloud is formed as a consequence of a large upward flux of sulfuric acid vapor from the evaporation region below the cloud base. The mechanism of lower cloud formation is probably heterogeneous nucleation of sulfuric acid and water vapors on soluble nuclei. Model altitude profiles of the abundances of water vapor and gaseous sulfuric acid demonstrate the control of these vapors by the condensational cloud. Cloud processes account for the observed decline in concentration of water vapor with altitude, from ≈30 ppm below the clouds to ≈10 ppm at 60-km altitude. The structure of the lower and middle clouds is strongly dependent on the eddy diffusion coefficient. Hence, changes in transport rates may explain the variations in cloud properties revealed by the Pioneer Venus and Venera probein situmeasurements as well as by Earth-based and Galileo near-infrared observations of the lower part of the Venus cloud.