Splicing is the removal of intron sequences from pre-mRNA by the spliceosome. 
Researchers working in multiple model organisms - notably yeast, insects and 
mammalian cells - have shown that pre-mRNA can be spliced during the process of 
transcription (i.e. co-transcriptionally), as well as after transcription 
termination (i.e. post-transcriptionally). Co-transcriptional splicing does not 
assume that transcription and splicing machineries are mechanistically coupled, 
yet it raises this possibility. Early studies were based on a limited number of 
genes, which were often chosen because of their experimental accessibility. 
Since 2010, eight studies have used global datasets as counting tools, in order 
to quantify co-transcriptional intron removal. The consensus view, based on four 
organisms, is that the majority of splicing events take place 
co-transcriptionally in most cells and tissues. Here, we discuss the nature of 
the various global datasets and how bioinformatic analyses were conducted. 
Considering the broad differences in experimental approach and analysis, the 
level of agreement on the prevalence of co-transcriptional splicing is 
remarkable.