In this work we study the peculiar role of gallium and nitrogen atoms in the growth of InGaN by Plasma Assisted Molecular Beam Epitaxy (PAMBE). We investigate growth of InGaN layers on vicinal GaN (0001) substrates. Indium incorporation as a function of gallium and nitrogen fluxes was examined. We propose a microscopic model of InGaN growth by PAMBE postulating different indium adatom incorporation mechanisms on two nonequivalent atomic step edges of wurtzite crystal. The role of gallium and nitrogen fluxes during the growth of InGaN layers is discussed. (c) 2013 Elsevier B.V. All rights reserved.