The primary function of mitochondria in eukaryotic cells is to produce ATP (adenosine triphosphate) through the process of cellular respiration. Often referred to as the "powerhouses" of the cell, mitochondria convert stored energy from nutrients into usable energy forms. This energy is essential for various cellular processes, including metabolism, growth, and maintenance. Mitochondria also play roles in regulating cellular metabolism and apoptosis, contributing to overall cell health and function.