Co-translational quality control is triggered as aresponse to translational stalling events. Yet, different molecular mechanisms are employed for the recognition of these stalls and to trigger downstream rescue and quality control pathways. While the recognition of individual stalled ribosomes is poorly understood, the use of collided ribosomes as a proxy for the recognition of translation problems in the cell is conserved from bacteria to humans1–3. In eukaryotes, co-translational quality-control processes triggered by ribosome collisions accomplish several tasks and eventually trigger stress response signalling pathways4. These tasks include the degradation of aberrant mRNAs, the degradation of potentially deleterious nascent peptides, the ribosomal subunit recycling and tRNA recycling. Collided eukaryotic ribosomes are cleared via subunit dissociation by the ribosome quality control trigger complex (RQT/ASCC)5,6. Subsequently, the ribosome-associated quality control takes place on the released large ribosomal subunit and ensures the degradation of the potentially toxic nascent peptide7. We mainly use structural analysis by cryo-EM to gain mechanistic understanding of these co-translational quality control events. To that end, we employ cell-free in vitrotranslation systems derived from bacteria, yeast and human cells in order to recapitulate ribosomal stalls and to isolate collided ribosomes. On this basis, we can reconstitute recognition, rescue and other processes in vitro. These processes include ubiquitination by Hel2 and ribosome dissociation by RQT in the yeast system or mRNA cleavage by the endonuclease SmrB in E. coli. Moreover, we use genomically tagged quality control factors as bait proteins for in vivoexpression and subsequent isolation of corresponding quality control intermediates after triggering ribosomal stalls. Resulting complexes are then used for structural cheracterization by single particle cryo-EM, which usually yields ensembles of structures representing distinct functional intermediates with specific conformation and/or composition8. The most recent findings elucidating the molecular mechanisms underlying co-translational quality control will be presented along with future plans in research of host-pathogen interactions involved in translation control.