We present a theory of spherical micelle formation from cationic amphiphiles in the absence and in the presence of DNA. The distribution of micelle sizes as well as the critical micelle and aggregation concentrations (cmc and cac) are calculated. Micelle formation is favored by the hydrophobic tails but disfavored by the entropic cost associated with counterion condensation. Counterion release drives the complexation between DNA and amphiphiles and causes micellation at a much smaller concentration than in the absence of DNA. The stiffness of double-stranded DNA favors the formation of large micelles leading to a bimodal distribution of micelle sizes.