Decomposition of fine-root litter is much less studied than that of foliar litter although fine root litter is a major contributor to litter input to the forest soil. This chapter is devoted to decomposition of root tips and fine roots. Root litter decomposition may be studied using litter bags, through following remaining root mass in soil cores, or by direct observation. Recent studies have allowed to set up a model for root tips’ decomposition. Also, substrate quality appears important for the decomposition of the finest roots and climate considerably less. Furthermore, the finest root tips appear to decompose and approach a limit value. Limit values for fine roots can be influenced by AUR concentration and N availability. For somewhat coarser roots, say 2 mm diameter or greater, climate may have an effect on decomposition. Root decomposition in climatic gradients has been related to mean annual temperature (MAT) and at a global level using several species there is also a positive response to calcium (Ca) concentration. Recent studies have allowed estimation of limit values for root litter decomposition.