Photoconductive crystals have been employed in various photo-detecting devices such as charge coupled devices, photoresistors and infrared-based photonic systems. The dark and photocurrent properties of single crystals grown by the SEST, SR, or other methods were analyzed using a Keithley 485 picoammeter under a DC electric field at room temperature, with a vacuum level of 1 × 10-7 m bar. Generally, for photoconductivity the crystal is coated with silver on opposite faces, and positioned between two copper electrodes and connected in series with a picoammeter. Initially, the dark current was measured without any exposure to light, across the applied field ranging from -5 to +5 V. Light from a 100 W halogen lamp containing iodine vapor was then focused on the sample using a convex lens, and the photocurrent was subsequently recorded. If the photocurrent is greater than the dark current it is called as positive photoconductive nature of the crystal, and if the dark current is greater than the photocurrent it is called as negative photoconductive nature. In this chapter, we examine how single crystals exhibit positive and negative photoconductivity, and explore their various applications. Crystals are used in a rangeof fields, including photodetectors, solar cells, optoelectronic devices, and photonic systems, where their photoconductive properties play a critical role.