This book mainly focuses on the understanding of basic concepts related Hydrodynamic Lubrication. In this more emphasis is given on steadily loaded oil film Journal Bearings. It includes discussion on derivation of generalised Reynold's equation for specific cases of Journal Bearing. In case of steadily loaded Journal Bearings viscosity is assumed to constant. But in reality because of rise in temperature, viscosity of oil film changes. In this book effect of variation of viscosity on the performance of Journal bearing is discussed. Plots of steady state, dynamic and thermo-hydrodynamic analysis are included in this book.