This paper is devoted to thermal spraying and presents the state of our current knowledge, as well as the research or development needs are in; spraying heat sources i.e., flame, HVOF, D-Gun, plasma torches; particle heat and momentum transfer (measurements and modeling), process on-line control, powder morphologies and injection within the hot jet and reactions with environment; coating formation i.e., particle flattening and solidification, splat layering, residual stresses, coating microstructure and properties; reliability and reproducibility of coatings.