High-throughput sequencing of transcripts through RNA-Seq has revolutionised the way gene expression can be understood. However, RNA-Seq only measures the steady-state levels of stably-expressed transcripts rather than the act of transcription. To measure nascent transcription, a range of sequencing methods have been developed, all with a range of different benefits and disadvantages. This study aims to advance the already established transient transcriptome sequencing (TT-Seq) approach and develop two novel nascent transcriptomic methods in human cells that utilise metabolic labelling and deliver high resolution profiles, called SNU-Seq (single nucleotide resolution 4sU-Seq), and size-selected SNU-Seq. The former is particularly well-suited to measure elongation of transcription throughout the gene body whereas the latter is used for studying transcription at the very 5’ end of genes. This study therefore includes a comprehensive analysis of promoter-proximal pausing behaviour and the development of a new size-selected SNU-Seq-based pipeline for annotations of actively-transcribed transcription start sites.