The Gordon Conference in Mammary Gland Biology focuses on normal mammary gland biology and breast cancer biology. This meeting is unique in that it brings together developmental and cancer biologists, with a focus not only on the normal development of the mammary gland and on important issues such as lactation, but also on how the biology of the normal mammary gland informs us about breast cancer biology. The consideration of normal mammary biology in breast cancer biology is a key component of this meeting, as issues such as those highlighted in our meeting below, are relevant to both the developing mammary gland and to breast tumor onset and progression. The 2017 meeting will focus on numerous cutting edge areas in the fields of mammary gland biology and neoplasia. These areas include niches in development and disease, stem cell biology, dormancy in treatment resistance and recurrence, heterogeneity in development and disease, epithelial cell plasticity, stromal determinants of epithelial cell behavior, as well as unconventional mechanisms controlling both organogenesis and carcinogenesis. The meeting has a longstanding tradition of excellent interactions across all levels of investigators, including graduate students and senior faculty members, and is renowned for its energetic discussions of cutting edge science, for interactive poster sessions, and for social time to increase interactions between all members attending. In addition, the meeting includes informal sessions to promote the careers of young scientists ("meet the expert" lunch sessions), with a specific afternoon session dedicated to issues faced by female scientists embarking on a career in science (the GRC "power hour"). The Mammary Gland Biology GRC will be preceded by a Mammary Gland Gordon Research Seminar (GRS) in which graduate students and post-doctoral fellows present their work in a forum prior to the arrival of their mentors. Students and post-docs are encouraged to apply to both meetings.