Transition metal-doped ZnO bulk crystals and thin films have been investigated to determine the effects of transition metal incorporation on optical, magnetic, and structural properties of ZnO. A modified melt growth technique was used to grow bulk Zn1-xMnxO, Zn1-xCoxO, and Zn1-xFexO. Optical transmission measurements show an apparent shift in absorption edge with increasing transition metal incorporation. Raman spectroscopy also shows increasing lattice disorder with increasing transition metal concentration. ZnO thin films doped with Ni, Co, and Gd were grown by metalorganic chemical vapor deposition (MOCVD). While the Co-doped thin films showed antiferromagnetic behavior, magnetic hysteresis was observed in the Ni-doped and Gd-doped thin films. Structural quality was verified with X-ray diffraction (XRD), and optical properties were investigated using room temperature photoluminescence (PL) and optical transmission measurements. Properties of ZnO:TM bulk crystals and thin films are compared and used to discuss possible origins of ferromagnetism in these materials.