Droplet size has significant scientific and industrial relevance in the effectiveness of atomization for several applications in the chemical, pharmaceutical, and food industries. This technology is widely employed in the food industry for processes such as spray drying, microencapsulation, edible coatings, and food disinfection, among others. This work comprehensively reviews the effect of liquid properties and equipment operating factors influencing droplet size in pneumatic and ultrasonic atomization. The discussion on the atomization theories includes the different models for estimating droplet size as a function of selected variables for both processes. The different model approaches are reviewed, focusing on their advantages, disadvantages, applications, and limitations. Furthermore, selected models were employed to carry out different sensitivity analyses showing the effect of variables related to the liquid properties, the type and characteristics of the atomizers, and the operating conditions, allowing the reader to appreciate the most critical factors in both atomization systems.