An ink set including an ink composition including resin particles, a colorant, and water, and a treatment solution including an anionic surfactant, water, and a compound configured to aggregate at least one of the colorant or the resin particles in the ink composition, in which the ratio of the content of the anionic surfactant with respect to the content of the compound configured to aggregate at least one of the colorant or the resin particles is 0.001 to 0.600 in terms of mass. An image forming method in which the ink set is used.