Fine needle aspiration cytology (FNAC), fine needle aspiration biopsy (FNAB) are non-invasive, safe, simple, rapid, cost-effective and popular diagnostic tools. Along with other biochemical, hematological, clinical and imaging techniques, these are two additional diagnostic modalities used for diagnosis and better management plan of different diseases. This chapter deals with indications of FNAC, FNAB, advantages and disadvantages, materials required for the tests, collection procedure, steps of staining and evaluation of smear. Commonly, FNAC and FNAB are performed on thyroid swelling, breast lump, salivary glands, lymph nodes, oral lesions and soft tissue tumors externally. Internal or guided FNAC (CT/USG) are done on deep lesions in lung, liver, GIT, intra-abdominal mass, kidney, adrenal and other organs.