Biopsy involves the removal of a tissue sample, laboratory analysis, and interpretation of the results. The usual objective of a biopsy is to establish or confirm a diagnosis. For example, intraocular biopsy is useful when clinical examination fails to distinguish a melanoma from a nevus or metastasis. Even when there is a confident clinical diagnosis, biopsy may be performed to determine the tumor subtype. A uveal tumor can be sampled by aspirational, incisional, or excisional biopsy techniques, depending on its size and location in the eye. Close collaboration with the cytopathologist is essential to ensure adequate sample size and handling. Aspiration biopsy is essentially contraindicated if retinoblastoma is a possibility. In this chapter, we review techniques, indications, complications, and the limitations of intraocular biopsies. Techniques for biopsy of conjunctival, eyelid, and orbital tumors are covered elsewhere in their respective volumes. Other biopsy techniques, such as incisional and excisional biopsy and diagnostic vitrectomy, are discussed elsewhere.