The influence of tumor infiltrating lymphocytes on tumor growth and response to therapy is becoming increasingly apparent. While much work has focused on the role of T cell responses in anti-tumor immunity, the role of B cells in solid tumors is much less understood. Tumor infiltrating B cells have been found in a variety of solid tumors, including breast, ovarian, prostate, melanoma, and colorectal cancer. The function of B cells in solid tumors is controversial, with many studies reporting a pro-tumor effect, while other studies demonstrate a role for B cells in the anti-tumor immune response. In this review, we discuss the prognostic ability of B cells in solid tumors as well as the mechanisms by which B cells can either promote or suppress anti-tumor immunity. Additionally, we review current therapeutic strategies that may target both pro- and anti-tumor B cells.