This review is subjected to impart light on the formation schemes of one ring aromatic compound to the polycyclic aromatic hydrocarbons (PAHs) and their further sequential growth into the first soot particle, i.e. soot nucleation. It mainly includes the role of stable and radical species in the formation of PAHs and soot. With some focus on limitations of previous results, new experimental investigations and related mechanisms are discussed in detail. A new and efficient kinetic mechanism for the formation of large PAHs via the active role of a phenyl radical, i.e. phenyl addition /cyclization (PAC), is proposed. An alternative mechanism, methyl addition/cyclization (MAC), is also proposed. This mechanism is especially applicable to the pyrolysis of aliphatics and alkylated aromatic hydrocarbons which produces methyl sufficient radicals. These new mechanisms are expected to be helpful especially for kinetic modeling in many theoretical works on hydrocarbons combustion. Recent progress in kinetic simulations of soot particle growth is also reviewed briefly.