Nanostructures used to build current technology devices are generally based on the stack of several thin films (from few nanometer-thick to micrometer-thick layers) having different physical properties (conductors, semiconductors, dielectrics, etc.). In order to build such devices, thin film fabrication processes compatible with the entire device fabrication need to be developed (each subsequent process step should not deteriorate the previous construction). Solid-state reactive diffusion allows thin film exhibiting good interfacial properties (mechanical, electrical…) to be produced. In this case, the film of interest is grown from the reaction of an initial layer with the substrate on which it has been deposited, during controlled thermal annealing. In the case of the reaction of a nano-layer (thickness < 100 nm) with a semi-infinite substrate, nanoscale effects can be observed: i) the phases appear sequentially, ii) not all the thermodynamic stable phases appear in the sequence (some phases are missing), and iii) some phases are transient (they disappear as fast as they appear). The understanding of the driving forces controlling such nanoscale effects is highly desired in order to control the phase formation sequence, and to stabilize the phase of interest (for the targeted application) among all the phases appearing in the sequence.This chapter presents recent investigations concerning the influence of atomic transport on the nanoscale phenomena observed during nano-film reactive diffusion. The results suggest that nano-film solid-state reaction could be controlled by modifying atomic transport kinetics, allowing current processes based on thin-film reactive diffusion to be improved.