Advancements in three-dimensional (3D) printing has expanded design freedom across various fields, including footwear. Driven by recent progress in biomechanics, footwear has increasingly adopted complex structural designs to meet diverse functional demands, ranging from personal activity to competitive athletics and medical rehabilitation. Accordingly, the role of 3D printing in footwear development has become increasingly significant. This review categorizes the functions of footwear into protection, performance enhancement, and therapeutic applications, and systematically explores the impact of 3D printing on each of these primary functions. 3D printing technology enables the fabrication of complex but mechanically efficient structures, while 3D scanning method facilitates the application of optimal, personalized designs tailored to individual biomechanics, which significantly impact all three functional areas of footwear. Such design advantages offered by 3D printing have been demonstrated across various fields, with both commercial and academic examples presented to support these findings. This review highlights interdisciplinary insights from biomechanics, ergonomics, and clinical studies to discuss the current status, limitations, and future potential of 3D-printed footwear. We conclude that continuous advancements in design methodology, material science, and printing technology will accelerate the adoption of 3D printing in next-generation footwear.