Multiphase flows and droplet dynamics play a vital role in the industry. Mineral ore (i.e., iron, aluminum, and copper mined in huge quantities yearly) must flow at some stage during extraction. Fluidized beds, bubbly flow in nuclear reactors, inkjet printing, gas-particle flows in chemical reactors, cavitating pumps and turbines, electrophotography used in copy machines, and laser and LED printers are a few examples of process technologies where multiphase flows play a vital role. The importance of multiphase flows concerning air pollution has recently been well recognized. In particular, in propulsion devices, such as automobiles and gas turbine engines in aircraft and power plants, the combustion of liquid fuels, such as diesel, gasoline, and Jet-A, is responsible for creating greenhouse gases and particulates (e.g., unburned carbon particles), which are identified as pollutants. The efficiency of the combustion process and, consequently, the production of the resulting pollutants are dictated by the breakup and vaporization of liquid fuels, making understanding these phenomena critical to developing efficient combustion devices. This ACS In Focus digital primer discusses the current understanding of the breakup and vaporization of single droplets in stagnant and convective environments. Its intended audience is an early career researcher (ranging from a second-year Ph.D. student to a postdoctoral fellow) interested in exploring the fascinating world of liquid droplets. The reader is expected to have had at least an advanced thermodynamics and fluid mechanics undergraduate course.