Numerous techniques have been described for monitoring the postoperative viability of microsurgical free tissue transfers, and their sensitivity and reliability continue to be evaluated in animal experiments and clinical trials. Relative advantages and disadvantages of these various postoperative monitoring techniques are discussed. The concept of intraoperative monitoring of the microsurgical anastomoses during closure and inset of a free flap is introduced because many free flaps may fail on the operating table, but this only becomes clinically apparent several hours later in the early postoperative period.