The most common surgical procedure in the United States is cataract surgery; most specifically, phacoemulsification. Understanding the fluidics and ultrasonic power fundamentals for phacoemulsification is instrumental for their safe and efficient use. Although phaco machines allow a few decades ago, the basic concepts have remained the same. Phaco machines allow ultrasonic-assisted aspiration of the cataract while maintaining the stability within the eye and minimizing the trauma of surgery to ocular structures. In this light, the two primary concepts are the fluidics of the lens aspiration and the application of the ultrasound power.