Prof. Doug Ruthven and Prof. Jörg Kärger are two giants in the field of zeolite science and engineering. Over their academic careers encompassing almost forty years each, they have contributed significantly to the advancement of fundamental understanding of adsorption and diffusion in zeolites as well as their industrial applications. The author, in the beginning of his academic career, had an opportunity to spend two years as a post-doctoral fellow in Prof. Ruthven’s laboratory at the University of New Brunswick (1975–1977). This experience actually motivated me to spend my academic career in working in the field of zeolite adsorption and diffusion. Nearly thirty years later, I spent a year as a Gast Mercator Professor at the University of Leipzig in the laboratory of Prof. Kärger (2005–2006). These two opportunities at two different ends of my academic career provided me with unique perspectives to reflect on the important contributions made by Professors Ruthven and Kärger to the field of zeolite science and technology. This article summarizes my personal perspectives on the breadth and depth of their contributions.