Three-dimensional (3-D) printing, also known as additive manufacturing, provides a novel and cost-effective approach for implementing microwave devices. With the rapid advancement and improved manufacturing resolution of the 3-D printing technology, additive manufacturing has enabled the design and fabrication of electronic devices in higher terahertz (THz) frequency bands, contributing to bridging the gap between microwaves and photonics. Simultaneously, metalenses have garnered significant attention due to their ability to shape electromagnetic (EM) wavefronts. Metalens technology offers a promising solution for wave focusing, surpassing traditional dielectric lenses with advantages such as reduced weight and low loss, particularly at THz frequencies. In this article, we present an overview of the development of 3-D-printed THz metalenses, ranging from single metalenses to dual-layer and trilayer configurations. The functionality of the metalenses becomes more powerful, from replacing conventional light-focusing dielectric lenses for single-layer metalenses, achieving 2-D beam scanning, holographic imaging, and reconfigurable orbital angular momentum (OAM) for dual-layer metalenses, to enabling 3-D focus scanning for trilayer metalenses. We also discuss practical measurement technologies for THz metalenses and briefly outline the prospective to propel the 3-D-printed metalens technology forward.