The work reporting a detailed and comparative study of Pb UPD and Pb e-less ML deposition on Ru(0001) substrate is presented. The electrochemical results are analyzed through the scope of the adsorption isotherm formalism where parameters describing the thermodynamics of deposited Pb monolayer obtained by each process are compared. In addition to these results, the in situ STM and electrochemical quartz micro balance data are presented for each process identifying the mutual mechanistic similarities and differences between electroless Pb and underpotential Pb monolayer. Considerable applications of Ru metal in microelectronics and catalysis rise significance of these results for variety of future developments in these areas. (c) The Author(s) 2019. Published by ECS.