R package stringgaussnet: PPI and Gaussian Network Construction from Transcriptomic Analysis Results Integrating a Multilevel Factor. A toolbox for a construction of protein-protein interaction networks through the ’STRING’ application programming interface, and an inference of Gaussian networks through ’SIMoNe’ and ’WGCNA’ approach, from DE genes analysis results and expression data. Additional functions are provided to import automatically networks into an active ’Cytoscape’ session.