Immunological regulation at the implantation site is a complex process, dysfunction may contribute to infertility, recurrent implantation failure (RIF) or recurrent pregnancy loss (RPL). Apart from endometrial NK and T cells, whose phenotypic profile and functional involvement have been recognised, evidence suggests that endometrial B cells may also have a potential role in reproductive pathologies. This thesis aimed to investigate endometrial immune profiles during human implantation, with a specific focus on the role of endometrial B cells. Both healthy women and infertility, RIF or RPL patients were recruited for endometrial immune profiling, focusing on cell proportions (NK, T and B cells) and activation status. Additionally, peripheral blood samples were collected and analysed in parallel. Significant differences were observed between peripheral and endometrial immune profiles, in minor cell populations like CD56bright CD16dim NK cells and CD4 CD8 double positive T cells, such differences were not previously reported. A standard operating protocol (SOP) was established so that comparison between controls and infertility, RIF or RPL patients could be made with more patients being enrolled in the near future. The role of B cells in the human endometrium was investigated. A systematic review was performed to understand the B cell involvement in reproductive pathologies. A number of immunohistochemistry studies were retrieved that identified endometrial B cells in association with T cells in 'lymphoid aggregates (LAs)', however, neither have been extensively characterised. RNA-sequencing and flow cytometric analysis were performed on CD19+ endometrial B cells. B cells comprised 1-5% of endometrial immune cells, the majority were naïve or memory B cells, with few plasma cells. Compared with circulating B cells, endometrial B cells had an activated phenotype, with increased expression of CD69, HLA-DR, CD74 and CD83, and IL-10 production capacities. PD1+CXCR5+ICOS+ T follicular helper-like cells and FAS+IgD- germinal centre-like B cells were present in the endometrium. Together with previously reported LAs, endometrial B cells may be an active player in shaping the endometrial immune environment.