The Diffusion Model Visualizer is a program allowing for studying the effect of the seven model parameters (a, z, v, t0, sz, sv, and st0) upon the response time density curves and positive/negative response probabilities. It supports interactive parameter change with immediate update of the diagram. The diagram can be stored to disk for further use (e.g., in an article or educational context). The program is freeware. For further information regarding technical details and usage see: [Alexandrowicz, R.W. (2020). The diffusion model visualizer: an interactive tool to understand the diffusion model parameters. *Psychological Research 84*(4), 1157–1165. https://doi.org/10.1007/s00426-018-1112-6] If you have any question regarding the program, pls. contact me via rainer.alexandrowicz [at] aau [dot] at. : https://link.springer.com/article/10.1007/s00426-018-1112-6 : http:// *Technical note: The program is currently available as a Windows program. Linux and Apple users require an emulator to run it.* **UPDATE Sept 2021: New Version 1.1 online!** Most significant change: *A new slider now allows for changing the intra-trial variance s^2*; several minor changes (see ABOUT).