 In vitro tumor models have been crucial for cancer research and drug screening, but lack understanding of metastasis, which is the primary cause of cancer-related deaths. To address this, these models have increased in complexity and diversified their output parameters to recapitulate critical steps in the metastatic cascade. Advances in tumor cell biology, 3D cell culture, tissue engineering, biomaterials, microfabrication, and microfluidics have enabled rapid development of new models that incorporate multiple cell types, extracellular matrix materials, and spatial and temporal introduction of soluble factors. The drive towards precision medicine has increased interest in adapting these models for patient-specific therapies, clinical management, and assessment of metastatic potential. This article was authored by Mariah E. Kat, Amanda E. Placone, Andrew E. Wong, and others.