In the last decade, we have seen rapid developments in metastable diamond synthesis by means of lowpressure chemical vapor deposition. Concurrently, a fast growing interest in diamond technology has emerged. This review discusses the various low-pressure growth methods of diamond films. Particular attention is paid to recent advances in the understanding of the mechanism of diamond nucleation and metastable growth. These advances are discussed in connection with the advances in diamond heteroepitaxy, which raises hopes that single crystalline diamond films are not far beyond reach. Modern surface science techniques applied to diamond study have played an essential role in these achievements and their contributions are discussed.