In 2022, an estimated 2.3 million new cases of breast cancer were reported globally, along with approximately 670,000 deaths, making it the most prevalent cancer among women worldwide. Breast cancer remains a leading cause of mortality among women worldwide, necessitating innovative strategies for early detection and effective treatment. Therefore, increasing the efficacy of the treatments while reducing their toxicity is of utmost importance to improve the quality of life for patients with breast cancer. Conventional therapeutic strategies often suffer from poor specificity, systemic toxicity, and multidrug resistance. In recent years, stimuli-responsive nanocarriers have emerged as a transformative approach for their structural ability, good biocompatibility, and biodegradability in targeted breast cancer therapy, offering enhanced precision in drug delivery. These stimuli-responsive nanocarriers can react to the intrinsic physicochemical and pathological conditions of diseased regions to improve the specificity of drug delivery. These smart nanocarriers are engineered to respond to specific internal (e.g., pH, redox potential, and enzymes) or external (e.g., temperature, light, and magnetic fields) stimuli prevalent in the tumor microenvironment (TME). By leveraging these cues, nanocarriers can selectively release therapeutic agents at the tumor site, minimizing damage to healthy tissues and improving treatment efficacy. This chapter reviews recent advancements in the design, functionalization, and application of stimuli-responsive nanocarriers for breast cancer treatment, highlighting their potential to overcome limitations of traditional therapies. It also addresses current challenges and prospects in translating these nanotechnologies from the laboratory to clinical practice.