Our research in cryptosporidiosis stems from identifying it as a major cause of diarrhea in our longitudinal community-based cohort studies of amebiasis. Diagnostic test development went hand-in-hand with studies in human cohorts, and encompassed qPCR, multiplex antigen detection, and point of care tests. Studies of the role of innate and acquired immunity in protection derived from the observation that not every infection caused diarrhea. Discoveries have included the importance of mannose binding lectin in innate protection, and the role of both class I and II MHC and of breast milk anti-cryptosporidium IgA for acquired immunity. Finally we have determined that cryptosporidiosis in the first two years of life is associated with malnutrition, as measured by stunting or linear growth shortfall.