Thin-film coatings are universal on optical components such as displays, lenses, mirrors, cameras, and windows and serve a variety of functions such as antireflection, high reflection, and spectral filtering. Designs can be as simple as a single-layer dielectric for antireflection effects or very complex with hundreds of layers for producing elaborate spectral filtering effects. Starting from basic principles of electromagnetics, design techniques are progressively introduced toward more intricate optical filter designs, numerical optimization techniques, and production methods, as well as emerging areas such as phase change materials and metal film optics. Worked examples, Python computer codes, and instructor problem sets are included. Key Features: Starting from the basic principles of electromagnetics, topics are built in a pedagogic manner toward intricate filter designs, numerical optimization and production methods. Discusses thin-film applications and design from simple single-layer effects to complex several-hundred-layer spectral filtering. Includes modern topics such as phase change materials and metal film optics. Includes worked examples, problem sets, and numerical examples with Python codes.