A single gene can give rise to multiple protein species, or proteoforms, by taking advantage of biological processes occurring before, during or after protein synthesis (Figure 1). These processes often yield altered protein starts that can influence protein function. For instance, alternative splicing or translation initiation can lead to distinct protein N-termini, while nascent polypeptide chains can be trimmed and N-terminally acetylated during translation. Also, after protein synthesis, protein termini can be recognized by modifying enzymes or by E3 ubiquitin ligases, the latter marking proteins for ubiquitin-dependent degradation by the N-degron pathways. Alternatively, protease processing can generate novel protein fragments (with new Nand C-termini) that can acquire specialized functions. A central method within protein N-terminal biology is positional proteomics, where peptides matching protein N-termini can be enriched and identified, thereby informing on the identity, modification status and intensity of protein N-termini within cells. N-terminal proteomics can be used to delineate alternative proteoforms (e.g. shaped by alternative splicing or translation initiation) or identify substrates of N-terminal modifying enzymes, proteases or N-degron pathways. In plants, our understanding of the extent and functional implications of protein termini and their corresponding proteoforms is still in its infancy. This Research Topic focuses on the closely intertwined research disciplines studying the generation, modification and function of protein N-termini in plants.