A three-dimensional printing system comprising: a print-medium receptacle configured to hold a quantity of print medium; an energy-source system configured to provide energy to a plurality of energy locations and comprising a plurality of energy sources; at least one energy-directing system wherein each energy-directing system comprises; an array of waveguides configured to direct energy from the plurality of energy locations along a plurality of propagation paths wherein each propagation paths extends through one of a plurality of energy locations; and wherein each waveguide is configured to direct energy from the plurality of energy locations through the waveguide along the plurality of propagation paths wherein each propagation path extends from the waveguide in a unique direction at least determined by one of the plurality of energy locations; a control system in communication with the energy-source system and configured to cause the array of waveguides of the at least one energy-directing system to deliver energy at a threshold intensity level to a plurality of selected intersections of a plurality of intersections of the plurality of propagation paths by operating the plurality of energy sources to provide energy along the plurality of propagation paths; wherein the print medium is configured to react when exposed to energy at the threshold intensity level; and wherein the plurality of selected intersections define a plurality of interior and exterior surfaces of a three-dimensional ("3D") object inside the receptacle. a print-medium receptacle configured to hold a quantity of print medium; an energy-source system configured to provide energy to a plurality of energy locations and comprising a plurality of energy sources; at least one energy-directing system wherein each energy-directing system comprises; an array of waveguides configured to direct energy from the plurality of energy locations along a plurality of propagation paths wherein each propagation paths extends through one of a plurality of energy locations; and wherein each waveguide is configured to direct energy from the plurality of energy locations through the waveguide along the plurality of propagation paths wherein each propagation path extends from the waveguide in a unique direction at least determined by one of the plurality of energy locations; an array of waveguides configured to direct energy from the plurality of energy locations along a plurality of propagation paths wherein each propagation paths extends through one of a plurality of energy locations; and wherein each waveguide is configured to direct energy from the plurality of energy locations through the waveguide along the plurality of propagation paths wherein each propagation path extends from the waveguide in a unique direction at least determined by one of the plurality of energy locations; a control system in communication with the energy-source system and configured to cause the array of waveguides of the at least one energy-directing system to deliver energy at a threshold intensity level to a plurality of selected intersections of a plurality of intersections of the plurality of propagation paths by operating the plurality of energy sources to provide energy along the plurality of propagation paths; wherein the print medium is configured to react when exposed to energy at the threshold intensity level; and wherein the plurality of selected intersections define a plurality of interior and exterior surfaces of a three-dimensional ("3D") object inside the receptacle. <EOS>