Despite the growing importance of frozen embryo transfer (FET) in the treatment of subfertility, there is little consensus on the best method for endometrial preparation. A properly powered randomized controlled trial is much needed to establish the best endometrial preparation protocol for FET cycles. The chapter discusses the topics of natural cycle frozen embryo transfer, modified natural cycle FET, stimulated cycle FET, hormone replacement FET cycle, etc. Hormone replacement cycle allows the couple to avoid some of the pitfalls associated with a natural cycle FET. In some women, gonadotropin-releasing hormone agonists may be given in addition to hormone replacement to suppress any hormone production by the ovaries, which may interfere with the treatment. Doing a progesterone assay before the start of progesterone in the cycle helps in identifying premature luteinization and cycle cancellation is recommended if the value is more than 0.5 ng/mL. Endometrial thickness and pattern still remain the most researched parameters for their predictive value in in vitro fertilization. Endometrial thickness can be improved by extending the estrogen administration. Monitoring the frozen embryo transfer cycle involves a baseline ultrasound for all the patients irrespective of the protocol used.