Remarkable techniques for the separation and detection of small quantities of analytes have been developed in recent years. However, it is still difficult to directly analyze species of interest in complex matrices. Although some methods have been reported for direct injection into an analytical instrument, removal of interfering substances during sample preparation is an important step in the analytical process. This procedure is usually tedious and time consuming. To reduce the tedium of this task and the time required for sample preparation, many unique extraction techniques have been introduced and applied to the analysis of substances in environmental, food, and biological samples. This chapter describes useful sample preparation techniques, including conventional and newly developed ones, for determining analytes of interest in biological, environmental, and food sources.