Fiber reinforced composites are prepared by embedding fibers into metal, polymer, and ceramic matrices. Often these fibers are coated with nanometer thick layer before embedding into matrices to improve performance, especially life-time of the composites. In general, coatings are prepared by sol-gel or chemical vapor deposition. However, these techniques have limitations such as two or more fibers are linked by deposited coating and also form non-uniform coating thickness on fiber, which affect the composite adversely. Atomic layer deposition (ALD) is one of the techniques which can overcome these problems because it can deposit very thin layer with uniform thickness. An ALD reactor has been designed, especially for meter long bundle of fibers. Various oxides have been deposited onto bundle of carbon fibers. Coatings were uniform, and it improve oxidation resistance of the fibers significantly. This book, therefore will provide a new direction for material science, especially for composites science and technology. It will help to design composites for high temperature applications.