Ca2+ influx through Ca2+ permeable ion channels is a key trigger and regulator of a diverse set of cellular events, such as neurotransmitter release and muscle contraction. Ca2+ influx is also a regulator of processes relevant to cancer, including cellular proliferation and migration. This review focuses on calcium influx in breast cancer cells as well as the potential for pharmacological modulators of specific Ca2+ influx channels to represent future agents for breast cancer therapy. Altered expression of specific calcium permeable ion channels is present in some breast cancers. In some cases, such changes can be related to breast cancer subtype and even prognosis. In vitro and in vivo models have now helped identify specific Ca2+ channels that play important roles in the proliferation and invasiveness of breast cancer cells. However, some aspects of our understanding of Ca2+ influx in breast cancer still require further study. These include identifying the mechanisms responsible for altered expression and the most effective therapeutic strategy to target breast cancer cells through specific Ca2+ channels. The role of Ca2+ influx in processes beyond breast cancer cell proliferation and migration should become the focus of studies in the next decade.