The chapter discusses the life cycle of spliceosomal snRNAs, from their transcription, nuclear export, and reimport to their assembly into the spliceosome. It highlights the complex process of splicing, which involves the assembly of a dynamic ribonucleoprotein (RNP) machine composed of five subunits and associated proteins. The biogenesis of spliceosomal snRNPs is a multi-step process that occurs in distinct subcellular compartments, with stable but inactive pre-RNPs maturing at different locations. The chapter also covers the role of Cajal bodies in RNP assembly and maturation, the involvement of the SMN complex in cytoplasmic RNP assembly, and the nuclear import and remodelling of RNP complexes. Additionally, it details the stepwise assembly of the spliceosome, the catalytic mechanisms of splicing, and the regulation of alternative splicing by cis-acting elements and trans-acting factors. The chapter concludes by emphasizing the need for further research to understand the complex dynamics and regulatory mechanisms of the spliceosome.The chapter discusses the life cycle of spliceosomal snRNAs, from their transcription, nuclear export, and reimport to their assembly into the spliceosome. It highlights the complex process of splicing, which involves the assembly of a dynamic ribonucleoprotein (RNP) machine composed of five subunits and associated proteins. The biogenesis of spliceosomal snRNPs is a multi-step process that occurs in distinct subcellular compartments, with stable but inactive pre-RNPs maturing at different locations. The chapter also covers the role of Cajal bodies in RNP assembly and maturation, the involvement of the SMN complex in cytoplasmic RNP assembly, and the nuclear import and remodelling of RNP complexes. Additionally, it details the stepwise assembly of the spliceosome, the catalytic mechanisms of splicing, and the regulation of alternative splicing by cis-acting elements and trans-acting factors. The chapter concludes by emphasizing the need for further research to understand the complex dynamics and regulatory mechanisms of the spliceosome.