An example of a fusing agent includes a tetraphenyldiamine-based dye, alkyldiphenyloxide disulfonate, 1-methyl-2-pyrrolidone, and a balance of water. The fusing agent excludes a strong reducing species. The fusing agent may be incorporated into a three-dimensional printing method or a three-dimensional printing system. In an example of the three-dimensional printing method, a polymeric or polymeric composite build material is applied. The fusing agent is selectively applied on at least a portion of the polymeric or polymeric composite build material. The polymeric or polymeric composite build material is exposed to electromagnetic radiation to fuse the portion of the polymeric or polymeric composite build material in contact with the fusing agent to form a layer.