Radius fillers for composite structures, composite structures that include the radius fillers, and systems and methods of forming the radius fillers. The systems and methods may be configured to create a pre-form that may be utilized to form a radius filler and/or create a radius filler from the pre-form. Creating the pre-form may include extending a plurality of lengths of composite tape from a composite tape source and receiving the plurality of lengths of composite tape in a pre-form forming structure, converging and/or otherwise combining the plurality of lengths of composite tape within the pre-form forming structure to produce the pre-form, and/or withdrawing the pre-form from the pre-form forming structure. Creating the radius filler from the pre-form may include receiving the pre-form in a radius filler forming structure and producing the radius filler from the radius filler forming structure.