Challenges continue to exist in developing a comprehensive theory of diffusion in liquid metals, despite the advancement of several semi-empirical and theoretical models. One major difficulty in developing a theory is that experimental data are not available for many pure metals and binary metal systems, and when they do exist, data are often inaccurate. In addition to challenges with data quality, where deemed reliable, existing data are typically reported over limited temperature and concentration intervals. In this thesis research, interdiffusion data was obtained for the binary Al-Cu system using the solid wire long capillary technique (SWLC), and molecular dynamics (MD) simulation with a concentration-dependent embedded atom method (CD-EAM) interatomic potential. In the SWLC experiments the interdiffusion coefficient was determined at temperatures of 993 K, 1023 K, 1073 K, 1123 K, and 1193 K, over an Al-rich concentration range limited by the liquidus of the binary phase diagram at the given temperature. For liquid Al~100Cu~0 (tracer), Al80Cu20, and Al60Cu40, the interdiffusion coefficient is well described by the Arrhenius relationship D_AlCu=D_0*exp(-Q_0/RT) over the temperature range, with best fit parameter values of Q_0 = 20.85 ± 4.49 kJ/mol, D_0 = 8.21 (+5.4, -3.26) x 10^-8 m^2/s, Q_0 = 34.41 ± 3.71 kJ/mol, D_0 = 2.84 (+1.47, -0.97) x 10^-7 m^2/s, Q_0 = 38.74 ± 8.01 kJ/mol, D_0 = 4.03 (+5.89, -2.39) x 10^-7 m^2/s, respectively. For the MD simulations, a new Al-Cu CD-EAM interatomic potential was developed that is suitable for the study of diffusion phenomena in the liquid state. Self- and interdiffusion coefficients were determined over a temperature interval of 993-1493 K. Simulations are performed for liquid Al99.999Cu0.001 (tracer), Al80Cu20, and Al60Cu40, and interdiffusion is described by Q_0 = 22.81 ± 0.27 kJ/mol, D_0 = 1.04 (+0.03, -0.03) x 10^-7 m^2/s Q_0 = 30.15 ± 0.49 kJ/mol, D_0 = 1.78 (+0.08, -0.08) x 10^-7 m^2/s, Q_0 = 37.01 ± 1.48 kJ/mol, D_0 = 3.29 (+0.52, -0.45) x 10^-7 m^2/s, respectively. The calculated values of the interdiffusion coefficients from the MD simulation are in good agreement with those obtained using the SWLC technique, supporting the accuracy of these new experimental findings. / February 2017