Presenting diffusion and mass transfer from both engineering and fundamental science perspectives, this book offers a comprehensive summary of the theory and applies that theory to obtain detailed solutions to a wide variety of problems. It covers conservation laws and field equations, boundary conditions, constitutive equations, parameters in constitutive equations, and mathematical solution methods including Green's functions. The authors pay particular attention to polymer mass transfer, and they also discuss the free-volume theory for prediction of self-diffusion coefficients. Problems analyzed include bubble dissolution, impurity migration in plastic containers, and drug delivery using polymers.