Electrochemical sensors have acquired considerable prominence for applications in environmental monitoring, healthcare diagnostics, and industrial safety owing to their rapid response, high sensitivity, and cost-effectiveness. Metal oxides as electrochemical sensors perform better as of their superior redox activity, electrical behavior, and chemical stability. Their electronic structure and defect chemistry, influencing the overall performance have been explained in this chapter. Further, basic concepts of electrochemical transduction are described for more clarification. This chapter elaborates that sensing capability improves with the addition of rare-earth dopants in metal oxides from the available literature, as it can alter lattice defects, improve electrical conductivity, and offer additional active sites for better catalytic efficacy and analyte absorption. Their applications in environmental monitoring, pollution detection, gas, and biosensing have been highlighted, along with their experimental data demonstrating improved sensitivity, selectivity, and stability. The overall chapter provides an insight for developing the next generation electrochemical sensor with enhanced performance from a technology perspective.