Having a clear influence on methodologies for the creation of efficient and reliable software, Floyd made lasting contributions to computer science across several areas. His contributions included the design of Floyd's algorithm, which efficiently finds all shortest paths in a graph, and work on parsing. In one isolated paper, he introduced the important concept of error diffusion for rendering images, also called Floyd–Steinberg dithering (though he distinguished dithering from diffusion).
A significant achievement was pioneering the field of program verification using logical assertions with the 1967 paper Assigning Meanings to Programs. This was an important contribution to what later became Hoare logic.