Diarrheal diseases are responsible for ten percent of all mortality in children under-five world-wide and even milder forms of intestinal infection have a long lasting impact on the nutritional state, disease susceptibility and growth of children. These relationships are complex and the underlying mechanisms are not fully understood. Significant advances have been made in protecting children from some of these infections through vaccination. Targeting emerging challenges, such as the protozoan parasite Cryptosporidium, is at the forefront of this effort. This symposium will explore how recent scientific advances in microbiology, immunology, and medicine can be used to understand and ultimately solve this important global problem.