Monocle is an analysis toolkit specifically designed for single-cell RNA-Seq experiments, running in the R language environment. Its core function is pseudotime analysis, which can infer cell development trajectories and differentiation paths based on single-cell transcriptome data, and reconstruct the dynamic process of cell state transitions. The 3rd version of Monocle has undergone comprehensive upgrades in terms of algorithms and visualization, supporting the processing of larger datasets. Besides pseudotime analysis, Monocle also provides functions such as differential expression analysis, cell clustering, and gene module identification. This tool is released through the Bioconductor channel and is widely used in the fields of developmental biology and stem cell research.