Margaret C. Kielian grew up in Omaha, Nebraska, the third of four children. Her father was an accountant with the Army Corps of Engineers; her mother was a homemaker. She became interested in science at an early age. She had a chemistry set that at one time caused an explosion, leaving a blob mark on the ceiling, and she had a fish tank that was a great source of protozoa that she liked to study under a microscope. Her parents were interested in and exposed her to many cultural things as well. Kielian attended Roman Catholic schools, where she found that she had some good teachers. Her physics and chemistry teacher and her biology teacher were very good, encouraging her curiosity and interest. Her family had hiking trips and picnics in national parks and forests, and these trips also stimulated her love of nature. A summer National Science Foundation program at the University of Kansas inspired her decision to become a microbiologist. She won a Betty Crocker scholarship which helped pay for college. Kielian attended the University of Nebraska, where she majored in microbiology. She considered Stanford and Rockefeller Universities for graduate school and was encouraged to attend Rockefeller. She worked in William Bowers' lab, then took a summer lab course at the Woods Hole Marine Biological Laboratory. Kielian discusses having and raising children while pursuing a science career and the challenges facing two-career couples. She talks about Zanvil A. Cohn, her thesis adviser. As she studied fusion of phagocytic vacuoles with lysosomes in the Cohn lab she became increasingly interested in molecular biology; she learned fluorescence polarization technique. Next Kielian went to the European Molecular Biology Laboratory and then the University of Helsinki as a visiting scientist to learn techniques for working with Semliki Forest virus (SFV). From Finland she went to Yale University for postdoc with Ari Helenius; there she worked with viruses with an altered pH threshold for fusion. Then Kielian's research focus shifted to conformational changes in the spike protein. She isolated the mutant virus fus-1, which turned out to be a useful pH probe for work on endocytosis. At that point Albert Einstein College of Medicine vigorously recruited Kielian. She set up her lab with funding from National Institutes of Health, American Cancer Society, and Pew Foundation. Kielian's interview continues with more discussion of her lab's work on fusion in the SFV spike protein; the role of cholesterol in SFV infection; her collaboration with Carolyn Machamer; keeping up with literature in the field; experiments that did not produce usable lab results; Marianne T. Marquardt's work on cholesterol-depleted cells in the exit pathway; and an unexpected finding in Kielian's work on virus assembly and fusion. Kielian points to her scientific role models and discusses the representation of women on the Einstein faculty. She concludes the interview by telling of her academic responsibilities.