Scripps College, Pitzer College, and Claremont McKenna College 1 article published in JoVE Biology Reconstituting and Characterizing Actin-Microtubule Composites with Tunable Motor-Driven Dynamics and Mechanics Mehrzad Sasanpour1, Daisy H. Achiriloaie1,2, Gloria Lee1, Gregor Leech1, Maya Hendija1, K. Alice Lindsay3, Jennifer L. Ross3, Ryan J. McGorty1, Rae M. Robertson-Anderson1 1Department of Physics and Biophysics, University of San Diego, 2W. M. Keck Science Department, Scripps College, Pitzer College, and Claremont McKenna College, 3Department of Physics, Syracuse University This paper presents protocols for engineering and characterizing tunable three-dimensional composite networks of co-entangled actin filaments and microtubules. Composites undergo active restructuring and ballistic motion, driven by myosin II and kinesin motors, and are tuned by the relative concentrations of actin, microtubules, motor proteins, and passive crosslinkers.