Breast cancer is among the most prevalent cancers in women, and early detection is pivotal for enhancing treatment efficacy. Biosensor technologies emerge as prospective alternatives for  early diagnosis of breast cancer due to the limitations of commercial diagnostic procedures, including invasiveness, high cost, and low sensitivity. Biosensors provide rapid, sensitive, and typically non-invasive identification of specific breast cancer biomarkers through the use of biological recognisers (such as enzymes, antibodies, DNA, and aptamers) and physical transducers (including electrochemical, optical, piezoelectric, and calorimetric methods). These technologies enable the successful detection of classical biomarkers such as Human epidermal growth factor receptor 2 (HER2), Cancer antigen 15-3 (CA 15-3), and Cancer antigen 125 (CA125), as well as novel biomarkers like microRNAs, circulating tumour cells (CTC), and exosomes. This chapter provides a detailed examination of biosensor technologies for the early diagnosis of breast cancer, including several biosensor types, their operational principles, bioengineering design methodologies, clinical applications, and prospective advancements.