Background: Oestrogen receptor α is a key biomarker for breast cancer, and the presence or absence of oestrogen receptor α in breast cancer influences the treatment regimens and patients’ prognosis. Oestrogen receptors α are activated after ligand binding, then translocate into the nucleus and activate the transcription of specific genes. This process is called the genomic effect of oestrogen receptor α. Oestrogen receptor α also has nongenomic effects that are exerted mainly in cytoplasm. Due to the important involvement of oestrogen receptor α in cell signalling, these receptors represent a key target for anticancer therapy. Purpose: Although oestrogen receptor α was discovered 60 years ago, the corresponding signalling pathways have not yet been fully described due to their complexity. With respect to the considerable extent of oestrogen receptor α signalling, covering all related information is beyond the scope of this review, which is focused mainly on recently discovered aspects of oestrogen receptor α function.