Human ehrlichioses are bacterial, tick-borne, newly emergent infectious diseases. The first human case of ehrlichiosis in the United States was described in 1987. The knowledge of these infectious diseases is still evolving even though they have been known as veterinary pathogens for almost a century. Diagnosis remains a challenge due to the nonspecific nature of clinical signs and symptoms. Indirect immunofluorescence assay serology is the gold standard for diagnosis. Tetracyclines are the drug of choice for treatment of human ehrlichioses.