Along the development of an organism, precursors cells within tissues become specified into distinct cell types. Research in the last decades has shown that many of such processes involve communication between cells, albeit others happen to be mainly cell-autonomous and random. Communication can happen through molecules which move across the tissue or by juxtacrine signaling. Here I will focus on patterning involving diffusion, presenting several theoretical approaches whose predictions are quantitatively compared to data in model organisms. First I will present a mechanism to drive self-confined expression through a diffusing activator. Afterwards I will introduce a new mechanism for diffusion to drive patterning in reaction-diffusion systems.