The goal of this training path is to train outstanding clinicians and investigators in the field of Infectious Disease of Immunocompromised Hosts including solid organ and stem cell transplant recipients and cancer patients. After the first year of general Infectious Diseases training, fellows in this track spend an additional 1-3 years of training that includes: 1) care for complex patients undergoing oncologic therapies, stem-cell and solid organ transplantation both in the outpatient and inpatient settings; 2) clinical and/or basic investigation into challenges in the care of this patient population (depending on the fellow’s background and interests); and 3) training in the design and conduct of clinical trials relevant to this patient population. Fellows in this track select to spend the majority of their time in a dedicated program at either the MGH or BWH-DFCI, under the mentorship of faculty members with specific areas of expertise. The training opportunities in this area available at each of the institutions. The interests of the faculty are described more below.