Rheumatoid arthritis is a chronic, systemic autoimmune disease in which sustained synovial inflammation drives progressive cartilage and bone destruction. The conventional pharmacological armamentarium, from methotrexate and glucocorticoids to biological and targeted synthetic disease-modifying agents, controls the disease in many patients but does so at the cost of systemic exposure, dose-limiting toxicity, and incomplete penetration of drug into the inflamed joint. Nanocarriers reframe this problem as one of delivery rather than of pharmacology. By exploiting the leaky, angiogenic vasculature of the inflamed synovium and the surface receptors of activated synovial macrophages, engineered nanoparticles concentrate a payload where the disease is active while sparing healthy tissue. This review synthesises the current evidence on smart nanocarriers for rheumatoid arthritis, defined as systems that combine joint-selective targeting with a microenvironment-triggered release that answers to the acidic, oxidative, and enzymatically active conditions of the arthritic joint. The major platforms are examined in turn: liposomes, polymeric nanoparticles and micelles, dendrimers, inorganic and hybrid particles, and the cell-membrane biomimetic carriers that now define the frontier of the field. The passive and active mechanisms of joint targeting are set out, and the stimuli-responsive chemistries that convert a carrier into a smart one are compared. Across preclinical models the direction of the evidence is consistent: targeted and responsive nanocarriers lower the effective dose, raise joint drug concentration, and reduce systemic toxicity relative to free drug. Yet the translational record remains thin, with few candidates advancing to controlled trials. The barriers to translation, from manufacturing reproducibility to the absence of validated imaging biomarkers, are analysed, and a set of concrete priorities is proposed to move the field from elegant preclinical demonstration to a licensed nanomedicine for rheumatoid arthritis.