DNA methylation is essential for normal mammalian development and plays critical roles in various biological processes, including genomic imprinting, X-chromosome inactivation and repression of transposable elements. Although DNA methylation patterns are relatively stable in somatic cells, global reprogramming of DNA methylation occurs during mammalian preimplantation development. Advances in DNA methylation profiling techniques have been revealing the DNA methylation dynamics in mammalian embryos. Recently, we and other groups reported genome-scale DNA methylation analyses of human oocytes and preimplantation embryos, highlighting both the similarities and differences in the DNA methylation dynamics between humans and mice. In this review, we introduce the current knowledge of DNA methylation dynamics during early mammalian development. We also discuss the possibility of the application of genome-scale DNA methylation analysis techniques to human gametes and embryos for diagnostic purposes.