Since its discovery in the early days of splicing research, U1snRNP has been recognized as a crucial player in the early stages of the splicing process. In particular, binding of U1snRNP to the 5'splice site of exons is a fundamental step in the formation of the early splicing complex and directs the subsequent assembly of the functional spliceosome. In recent years, the way that the U1snRNP molecular complexes recognize real 5' ss sequences from a huge background of similar decoy sequences has been extensively studied. In this review, we will provide an account of the latest functional properties of U1snRNP as a splicing factor, its role in transcriptional and mRNA degradation processes, and how these properties can be exploited to act as prospective therapeutic or gene silencing strategies. Finally, we will discuss the latest experimental evidence that challenges the absolute requirement of U1snRNP presence for splicing to take place.