This paper summarizes recent studies of a variety of atmospheric phenomena in different parts of the world using the Penn State/NCAR mesoscale model. These phenomena include explosive cyclogenesis over the North Pacific and North Atlantic oceans, cyclogenesis over Europe and associated ozone transport during the ALPEX experiment, heavy rainfall and flash flood events over Pennsylvania and China, “Plateau” and “Southwest” vortices over China, severe storms over the United States, mesoscale convective complexes, elevated mixed layers and “lids,” an Australian Southerly Buster, low-level damming of cold air to the east of the United States Appalachian Mountains in winter, urban heat island effects, and regional acid deposition. This paper also reviews Observing System Simulation experiments (OSSEs), several sensitivity studies, the nesting of the mesoscale model in a global climate model for regional climate studies, and some recent real-time forecasting studies conducted by The Pennsylvania State University. An important result of these and earlier studies is that a general mesoscale model with realistic treatment of surface conditions and physical processes, and initialized with good large-scale conditions is capable of simulating and predicting a large variety of synoptic and mesoscale phenomena in different parts of the world. The model simulations also provide high-resolution, dynamically consistent data sets which are useful in understanding the physical behavior of complex mesoscale systems.