Experimental data on the synthesis of crystalline Cu, Cu2O, and CuO nanoparticles obtained earlier by the vapor-phase decomposition of copper(II) acetylacetonate (Cu(acac)2) were systematized and generalized. Studies were performed using a laminar flow reactor at atmospheric pressure within the ranges of precursor partial vapor pressure Pprec = 0.06-44 Pa and reactor temperature from 432 to 1216°C. The decomposition of Cu(acac)2 was studied in an inert nitrogen atmosphere and in the presence of various reagents (water vapors, H2, O2, and CO). The composition of synthesized particles varied from pure copper to its oxides (Cu2O and CuO) depending on experimental conditions and used reagents. A semi-empirical kinetic model was proposed for describing the product dynamics. The hypothesis on the predominant role of copper dimers in a particle's growth was stated. It was established that the composition of products is determined by the surface reactions on growing particles and is dependent on the ratio between the concentrations of the gaseous reagents. Calculated phase diagrams of the products of Cu(acac)2 decomposition in the presence of various reagents were in good agreement with experimental data. The proposed method of construction of the phase diagram of decomposition products can be employed for other systems. It was established that, upon the Cu(acac)2 decomposition in the presence of CO, carbon nano-onions were formed in addition to copper nanoparticles.