Eileen T. Lake, PhD, RN, FAAN is an international leader in the theory and methods of nursing systems research. Over nearly three decades of research, she has studied hospitals as complex organizations and focused on measuring elements of the nurse work environment and nurse staffing, and analyzing their relationship to safety and quality of care and patient outcomes. She developed and oversees the National Quality Forum-endorsed Practice Environment Scale of the Nursing Work Index, a survey measure. Translated into 23 languages, this instrument assesses the presence of features in the work environment that support professional nursing practice and has generated global evidence showing care settings that capitalize on nurses’ education and skills—by providing competent and supportive managers, expecting physicians to treat nurses as partners in care, providing sufficient staff and resources, and encouraging nurse input on decisions—achieve higher quality outcomes. The majority of her work over the past decade has focused on linking nursing system factors such as staffing and the work environment to outcomes of very low birth weight infant outcomes in the neonatal intensive care unit. She has begun to explore how work environments and nurse staffing influences obstetric outcomes and outcomes for newborns with neonatal abstinence syndrome, both complex populations in which a nurse is the principal care provider.