3D printing at the macroscale has evolved from making plastic prototypes to the production of high-performance functional metal parts for industries such as medical and aerospace. By contrast, MEMS devices today are produced in large quantities using semiconductor manufacturing processes. However, the semiconductor manufacturing paradigm is not cost-effective for producing customized MEMS devices in small to medium volumes (tens to thousands of units per year), and related applications are difficult to address efficiently. 3D printing of functional MEMS devices could play an important role in filling this gap. Here, we discuss recent advances in 3D- printed functional MEMS, addressing the challenges of economical customization at smaller production volumes.