Breast core needle biopsy (CNB) is the method of choice for establishing preoperative diagnosis. The clinical and imaging findings should be considered at the time of assessing any CNB. We discuss the diagnostic prowess of breast CNB and the variety of ancillary biomarkers that are routinely performed. This chapter also touches upon several diagnostic traps faced by pathologists while evaluating malignant, intermediate, and benign breast masses. Diagnosis should be established keeping in mind the limited nature of the sampling, making it prudent to err on the conservative side when faced with uncertain or equivocal findings. Finally, CNB histopathology along with clinical and radiological features forms the three pillars guiding the appropriate next step for patient management.