The book Factors of Soil Formation. A System of Quantitative Pedology published in 1941 represented a quantum leap forward in our understanding of the impacts of parent material, climate, topography, vegetative cover and time on soil character. Even after more than 50 yr, Hans Jenny's elegant theory of soil formation remains the foundation of modern thought regarding soil genesis. This SSSA Special Publication includes papers presented at a special symposium commemorating the 50th anniversary of the publication of Factors of Soil Formation held during the 1991 annual meeting of the Soil Science Society of America.