Ultrathin silicon die is a key enabler for high performance semiconductor devices and ultrathin packaging. The quality of ultrathin wafers and dies has a significant influence on packaging assembly yield and device reliability. The key quality characteristics of ultrathin wafers and dies are bow/warpage, total thickness variation (TTV), subsurface damage (SSD), surface roughness, and mechanical strength. Wafer and die bow/warpage cause handling and processing problems in manufacturing processes, and induce defects during various packaging assembly processes that eventually lead to device reliability issues. The wafer TTV requirement is becoming more stringent for new generations of thin and 3-D packages. SSD, surface roughness, and dicing defects have adverse effects on die mechanical strength and reliability. Therefore, characterization methods are needed for these quality characteristics to control the manufacturing processes for ultrathin wafers and dies to ensure good device performance and reliability. The following ultrathin wafer and die characterization techniques are discussed in this paper: noncontact bow/warp/TTV measurement, materialographic analysis with optical and electron microscopy, high-resolution X-ray diffraction, micro-Raman spectroscopy, scanning infrared depolarization, optical profilometry, atomic force microscopy, and uniaxial/biaxial bending tests.