Methods of three-dimensional printing can include iteratively applying a polymer build material as individual layers to a powder bed, where the polymer build material includes from about 80 wt % to 100 wt % polymer build particles, and based on a three-dimensional object model, selectively applying a binder agent including an aqueous liquid vehicle and polymer binder particles onto the individual layers of the polymer build material. The polymer binder particles have or are capable of having a melting temperature lower than a melting temperature of the polymer build particles. The methods can include exposing the powder bed to heat at a temperature less than a melting point of the polymer build particles but greater than a melting temperature of the polymer binder particles. The heat causes the polymer binder particles to melt to adhere the polymer build particles together to form a three-dimensional object.