This work is devoted to the discoveries and/or knowledge developed in the past years in the area of the application of heterogeneous catalysts containing niobium for selective oxidation in gas and liquid phases by the use of different oxidants. This book presents a general overview of the role of niobium species located in crystalline and amorphous solids in catalytic oxidation processes. The important ability of niobium to combine with many elements to form new compounds determines the unique properties of niobium containing catalysts. Two main roles of niobium species in heterogeneous catalysis are considered: as catalytic active centers and as promoters..