Electrochromics is a healthy blend of basic physics and chemistry, thin film science, device technology and market opportunities. Use of electrochromic (EC) materials as smart windows in an interactive architecture of buildings provide a better option for energy saving. Hence developments in electrochromics will remain a vital field for endeavors of various kinds in coming years. Molybdnum oxide (MoO3) shows pronounced electrochromism due to its interesting structural(provides conduits for intercalation/deintercalation) and electronic properties. It is a 4d transition metal oxide, which can be switched between two different optical states (transparent and colored) by Photochromic, Thermochromic or Electrochromic effect. This book presents a novel route of cathodic electrodeposition of hydrous MoO2 thin films and their thermal oxidation to obtain electrochromic MoO3 thin films. The fundamentals of Electro-deposition and material formation are discussed at length. structural, optical and electrochromic properties are studied and reasons for enhancement in Electrochromic parameters on the basis of proposed theories is discussed at length.