This chapter describes fine needle aspiration cytology (FNA), which allows the sampling of various solid tissues in the body with the aid of a fine needle. It considers FNA as a safe diagnostic procedure wherein significant complications are rare, distinguishing it as cost effective, acceptable to patients, and suitable for rapid and accurate diagnosis. It also points out that FNA is not a replacement for surgical histopathology or core biopsy as there are times where cytology cannot give a definitive answer and histological assessment is required. The chapter details the on-site assessment of FNA sample adequacy by a cytopathologist or trained biomedical scientist, which provides the optimal approach for obtaining adequate material for immediate investigation, ancillary testing, and eventual accurate diagnosis. It explains how deep lesions can be sampled with FNA with the aid of ultrasound or CT imaging for guidance.